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Merge pull request #3 from algorithm001/master · algorithm001/algorithm@e45d4cd · GitHub

Merge pull request #3 from algorithm001/master · algorithm001/algorithm@e45d4cd · GitHub
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xuyunbo
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Merge pull request #3 from algorithm001/master
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2 parents 693ee4a + e07e9d3 commit e45d4cd

368 files changed

Lines changed: 15957 additions & 23 deletions

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‎2019.04.27线上答疑要点整理.pdf‎

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‎README.md‎

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## 注意事项
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1. **代码文件命名规则：**`LeetCode_题目序号_学号`，比如学号为 `0` 的学员完成 [LeetCode 的第 2 题](https://leetcode.com/problems/add-two-numbers/description/) 后，请将代码文件名保存为 `LeetCode_2_0.py` (假设你使用的是 Python 语言)。
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1. **代码文件命名规则：**`LeetCode_题目序号_学号`，比如学号为 `0` 的学员完成 [LeetCode_33_108 的第 2 题](https://leetcode.com/problems/add-two-numbers/description/) 后，请将代码文件名保存为 `LeetCode_2_0.py` (假设你使用的是 Python 语言)。
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2. **作业公布地址：** 我们会在置顶的 issue 中公布当周的算法练习题以及其他注意事项。
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3. 如果对 Git 和 GitHub 不太了解，请参考 [Git 官方文档](https://git-scm.com/book/zh/v2) 或者极客时间的[《玩转 Git 三剑客》](https://time.geekbang.org/course/intro/145)视频课程。

‎Week_01/id_100/LeetCode_21_100.java‎

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/**
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* Definition for singly-linked list.
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* public class ListNode {
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* int val;
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* ListNode next;
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* ListNode(int x) { val = x; }
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* }
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*/
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class Solution {
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public ListNode mergeTwoLists(ListNode n1, ListNode n2) {
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ListNode result = new ListNode(0);
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ListNode n0 = result;
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while (n1 != null && n1 != null) {
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//System.out.println("n1-----" + n1.val + "--------n2-------" + n2.val
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if (n1.val < n2.val) {
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n0.next = new ListNode(n1.val);
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n1 = n1.next;
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} else {
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n0.next = new ListNode(n2.val);
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n2 = n2.next;
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}
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n0 = n0.next;
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}
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if(n1 != null) n0.next = n1;
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else n0.next = n2;
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return result.next;
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}
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}

‎Week_01/id_100/LeetCode_83_100.java‎

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/**
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* Definition for singly-linked list.
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* public class ListNode {
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* int val;
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* ListNode next;
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* ListNode(int x) { val = x; }
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* }
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*/
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class Solution {
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public ListNode deleteDuplicates(ListNode head) {
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ListNode pre = head;
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ListNode pre_next = pre.next;
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if(pre == null || pre_next == null){
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return head;
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}
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while(pre_next != null){
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if(pre.val == pre_next.val){
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pre_next = pre_next.next;
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pre = pre_next;
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}else{
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pre = pre_next;
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pre_next = pre_next.next;
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}
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}
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return head;
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}
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}

‎Week_01/id_108/LeetCode_153_108.java‎

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/**
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* @author zhangruihao.zhang
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* @version v1.0.0
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* @since 2019/04/24
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*/
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public class LeetCode_153_108 {
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class Solution1 {
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public int findMin(int[] nums) {
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if(nums.length == 1){
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return nums[0];
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}
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if(nums.length == 2){
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return nums[0] > nums[1] ? nums[1] : nums[0];
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}
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if(nums[0] < nums[nums.length-1]){
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return nums[0];
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}
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int min = 0;
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int high = nums.length - 1;
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int mid = 0;
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while(min <= high){
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//针对1、2、3这种情况
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if(min == high){
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return nums[min];
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}
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mid = min + ((high-min) >> 1);
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if(nums[mid] > nums[high]){
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if(nums[mid+1] < nums[mid]){
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return nums[mid+1];
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}
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min = mid + 1;
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continue;
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}
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if(nums[mid] < nums[min]){
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if(nums[mid-1] > nums[mid]){
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return nums[mid];
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}
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high = mid - 1;
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}
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}
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return -1;
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}
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//二分查找
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//分为两种情况
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//mid比最后一个元素大，判断它右边的值是否小于它，如果小于的话就返回右边的值，否则的话，min取mid+1
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//mid比第一个元素小，判断它左边的值是否比它大，如果大的话，直接返回它自己，否则的话high取mid-1
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}
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class Solution2 {
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public int findMin(int[] nums) {
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if(nums.length == 1){
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return nums[0];
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}
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int min = 0;
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int high = nums.length - 1;
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int mid = 0;
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while(min < high){
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mid = min + ((high-min) >> 1);
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if(nums[mid] > nums[high]){
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min = mid + 1;
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} else {
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high = mid;
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}
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}
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return nums[min];
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}
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//二分查找
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//分为两种情况
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//mid比最后一个元素大，判断它右边的值是否小于它，如果小于的话就返回右边的值，否则的话，min取mid+1
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//mid比第一个元素小，判断它左边的值是否比它大，如果大的话，直接返回它自己，否则的话high取mid-1
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}
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}

‎Week_01/id_108/LeetCode_20_108.java‎

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import org.junit.Test;
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import java.util.Stack;
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/**
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* @author zhangruihao.zhang
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* @version v1.0.0
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* @since 2019/04/29
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*/
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public class LeetCode_20_108 {
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public static void main(String[] args) {
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String str = "()[]{}";
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System.out.println(isValid(str));
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}
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public static boolean isValid(String s) {
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Stack stack = new Stack();
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for(int i=0;i<s.length();i++){
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char c = s.charAt(i);
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if(stack.peek().equals(anotherChar(c))){
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stack.pop();
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}else{
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stack.push(c);
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}
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}
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return stack.isEmpty();
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}
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private static char anotherChar(char c){
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if(c == '('){
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return ')';
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}
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if(c == ')'){
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return '(';
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}
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if(c == '{'){
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return '}';
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}
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if(c == '}'){
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return '{';
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}
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if(c == '['){
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return ']';
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}
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if(c == ']'){
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return '[';
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}
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return '0';
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}
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}

‎Week_01/id_108/LeetCode_33_108.java‎

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/**
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* @author zhangruihao.zhang
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* @version v1.0.0
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* @since 2019/04/29
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*/
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public class LeetCode_33_108 {
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class Solution {
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public int search(int[] nums, int target) {
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if(nums == null || nums.length == 0){
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return -1;
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}
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if(nums[0] == target){
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return 0;
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}
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if(nums[nums.length - 1] == target){
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return nums.length - 1;
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}
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int end = nums.length - 1;
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int min = min(nums);
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//如果没有旋转，并且最大的数小于target
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if(min == 0 && nums[end]<target){
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return -1;
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}
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if(nums[end] > target){
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//target处于旋转的后半段
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return binarySerach(nums,min,end,target);
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}else{
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//target有可能处于旋转的前半段
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return binarySerach(nums,0,min-1,target);
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}
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}
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//查找旋转点
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private int min(int[] nums){
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int low = 0;
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int high = nums.length - 1;
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int mid;
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while(low < high){
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mid = low + ((high-low)>>1);
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if(nums[mid]>nums[high]){
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low = mid + 1;
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}else{
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high = mid;
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}
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}
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return low;
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}
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//二分查找
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private int binarySerach(int[] nums,int left,int right,int target){
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int mid = 0;
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while(left<right){
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mid = left + ((right - left)>>1);
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if(nums[mid]==target){
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return mid;
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}
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if(nums[mid]<target){
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left = mid + 1;
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continue;
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}
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if(nums[mid]>target){
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right = mid - 1;
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continue;
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}
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}
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if(nums[left] == target){
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return left;
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}
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return -1;
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}
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}
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}

‎Week_01/id_108/LeetCode_503_108.java‎

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import java.util.Stack;
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/**
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* @author zhangruihao.zhang
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* @version v1.0.0
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* @since 2019/04/29
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*/
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public class LeetCode_503_108 {
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class Solution {
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public int[] nextGreaterElements(int[] nums) {
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Stack<Integer> stack = new Stack<>();
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int index[] = new int[nums.length];
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for (int i = 0; i < index.length; i++) {
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index[i] = -1;
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}
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if (nums.length == 1) {
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return index;
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}
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int count = 0;
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while (count < 2) {
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for (int i = 0; i < nums.length; i++) {
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while (!stack.isEmpty() && nums[i] > nums[stack.peek()]) {
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index[stack.pop()] = nums[i];
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}
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stack.push(i);
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}
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count++;
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}
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return index;
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}
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}
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}

‎Week_01/id_108/LeetCode_687_108.java‎

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/**
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* @author zhangruihao.zhang
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* @version v1.0.0
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* @since 2019/05/03
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*/
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public class LeetCode_687_108 {
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/**
8+
* Definition for a binary tree node.
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* public class TreeNode {
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* int val;
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* TreeNode left;
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* TreeNode right;
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* TreeNode(int x) { val = x; }
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* }
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*/
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class Solution {
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int maxLen = 0;
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public int longestUnivaluePath(TreeNode root) {
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if(root == null){
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return 0;
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}
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longest(root);
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return maxLen;
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}
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private int longest(TreeNode root){
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if(root == null){
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return 0;
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}
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int leftLen=longest( root.left);
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int rightLen=longest( root.right);
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int leftUnivalueLen = 0;
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int rightUnivalue = 0;
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if(root.left != null && root.left.val == root.val){
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leftUnivalueLen = leftLen + 1;
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}
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if(root.right != null && root.right.val == root.val){
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rightUnivalue = rightLen + 1;
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}
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maxLen = max(maxLen , leftUnivalueLen + rightUnivalue );
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return max(leftUnivalueLen,rightUnivalue);
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}
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private int max(int x,int y){
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return x>y ? x : y;
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}
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}
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}

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