JavaArithmetic/src/datastructure/queue/LoopQueue.java at master · git-jhy/JavaArithmetic · GitHub

Repository navigation

History

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

package datastructure.queue;

import java.util.ArrayList;

import java.util.List;

import javafx.util.Pair;

/// Leetcode 102. Binary Tree Level Order Traversal

/// https://leetcode.com/problems/binary-tree-level-order-traversal/description/

/// 二叉树的层序遍历

///

/// 二叉树的层序遍历是一个典型的可以借助队列解决的问题。

/// 该代码主要用于使用Leetcode上的问题测试我们的LoopQueue。

/// 对于二叉树的层序遍历，这个课程后续会讲到。

/// 届时，同学们也可以再回头看这个代码。

/// 不过到时，大家应该已经学会自己编写二叉树的层序遍历啦：）

class Solution{

/// Definition for a binary tree node.

private class TreeNode {

int val;

TreeNode left;

TreeNode right;

TreeNode(int x) { val = x; }

}

private interface Queue<E> {

int getSize();

boolean isEmpty();

void enqueue(E e);

E dequeue();

E getFront();

}

private class LoopQueue<E> implements Queue<E> {

private E[] data;

private int front, tail;

private int size; // 有兴趣的同学，在完成这一章后，可以思考一下：

// LoopQueue中不声明size，如何完成所有的逻辑？

// 这个问题可能会比大家想象的要难一点点：）

public LoopQueue(int capacity){

data = (E[])new Object[capacity + 1];

front = 0;

tail = 0;

size = 0;

}

public LoopQueue(){

this(10);

}

public int getCapacity(){

return data.length - 1;

}

@Override

public boolean isEmpty(){

return front == tail;

}

@Override

public int getSize(){

return size;

}

@Override

public void enqueue(E e){

if((tail + 1) % data.length == front)

resize(getCapacity() * 2);

data[tail] = e;

tail = (tail + 1) % data.length;

size ++;

}

@Override

public E dequeue(){

if(isEmpty())

throw new IllegalArgumentException("Cannot dequeue from an empty queue.");

E ret = data[front];

data[front] = null;

front = (front + 1) % data.length;

size --;

if(size == getCapacity() / 4 && getCapacity() / 2 != 0)

resize(getCapacity() / 2);

return ret;

}

@Override

public E getFront(){

if(isEmpty())

throw new IllegalArgumentException("Queue is empty.");

return data[front];

}

private void resize(int newCapacity){

E[] newData = (E[])new Object[newCapacity + 1];

for(int i = 0 ; i < size ; i ++)

newData[i] = data[(i + front) % data.length];

data = newData;

front = 0;

tail = size;

}

@Override

public String toString(){

StringBuilder res = new StringBuilder();

res.append(String.format("Queue: size = %d , capacity = %d\n", size, getCapacity()));

res.append("front [");

for(int i = front ; i != tail ; i = (i + 1) % data.length){

res.append(data[i]);

if((i + 1) % data.length != tail)

res.append(", ");

}

res.append("] tail");

return res.toString();

}

public List<List<Integer>> levelOrder(TreeNode root) {

ArrayList<List<Integer>> res = new ArrayList<List<Integer>>();

if(root == null)

return res;

// 我们使用LinkedList来做为我们的先入先出的队列

LoopQueue<Pair<TreeNode, Integer>> queue = new LoopQueue<Pair<TreeNode, Integer>>();

queue.enqueue(new Pair<TreeNode, Integer>(root, 0));

while(!queue.isEmpty()){

Pair<TreeNode, Integer> front = queue.dequeue();

TreeNode node = front.getKey();

int level = front.getValue();

if(level == res.size())

res.add(new ArrayList<Integer>());

assert level < res.size();

res.get(level).add(node.val);

if(node.left != null)

queue.enqueue(new Pair<TreeNode, Integer>(node.left, level + 1));

if(node.right != null)

queue.enqueue(new Pair<TreeNode, Integer>(node.right, level + 1));

}

return res;

}

JavaArithmetic/src/datastructure/queue/LoopQueue.java at master · git-jhy/JavaArithmetic · GitHub

Repository navigation

Expand file tree

Breadcrumbs

LoopQueue.java

Latest commit

History

Breadcrumbs

LoopQueue.java

File metadata and controls