algorithm/Week_02/id_26/Leetcode_236_26.java at master · feixiangcode/algorithm · GitHub

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package com.fanlu.leetcode.binarytree;

// Source : https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/

// Id : 236

// Author : Fanlu Hai

// Date : 2018-04-24

// Other : lowest common ancestor (LCA): The lowest common ancestor is defined between two nodes p and q

// as the lowest node in T that has both p and q as descendants

// (where we allow a node to be a descendant of itself).

// Tips :

import java.util.LinkedList;

import java.util.Queue;

/**

* Definition for a binary tree node.

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

* TreeNode(int x) { val = x; }

* }

public class LowestCommonAncestorOfABinaryTree {

private TreeNode ans;

// This answer is copied from leetcode submission analysis sample

// 100.00% (20% faster than original) 44.21%

public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {

this.recurse(root, p, q);

return this.ans;

}

private boolean recurse(TreeNode node, TreeNode p, TreeNode q) {

if (node == null) {

return false;

}

// rec left

// it's very hard for me to write below code even though it's nothing hard.

int left = this.recurse(node.left, p, q) ? 1 : 0;

int right = this.recurse(node.right, p, q) ? 1 : 0;

int mid = (node == p) || (node == q) ? 1 : 0;

// this is better than comparing objects

if (mid + left + right >= 2) {

this.ans = node;

}

return (mid + left + right > 0);

}

//65.83% 40.60%

// this is fast enough to my understanding, but there are more elegant and faster ways to do the same steps

public TreeNode lowestCommonAncestorOriginal(TreeNode root, TreeNode p, TreeNode q) {

if (null == root || root == p || root == q)

return root;

TreeNode left = lowestCommonAncestorOriginal(root.left, p, q);

TreeNode right = lowestCommonAncestorOriginal(root.right, p, q);

if (null != left && null != right) {

return root;

} else if (null == right) {

return left;

} else {

// null == left

return right;

}

//return left == null ? right : right == null ? left : root;

}

/**

* below are some no very successfull attampts

Queue<TreeNode> pNodeList = new LinkedList<>();

Queue<TreeNode> qNodeList = new LinkedList<>();

//! Time Limit Exceeded

public TreeNode lowestCommonAncestorTooSlow(TreeNode root, TreeNode p, TreeNode q) {

TreeNode result = root;

dfsNode(root, p, q, new LinkedList<TreeNode>());

while (!pNodeList.isEmpty()) {

TreeNode tmp = pNodeList.poll();

// System.out.println(tmp);

if (tmp != qNodeList.poll()) {

break;

}

result = tmp;

}

return result;

}

public void dfsNode(TreeNode treeNode, TreeNode p, TreeNode q, Queue<TreeNode> queue) {

if (null == treeNode)

return;

Queue<TreeNode> tmpQueue = new LinkedList<>();

tmpQueue.addAll(queue);

tmpQueue.add(treeNode);

if (treeNode.val == p.val) {

pNodeList = tmpQueue;

}

if (treeNode.val == q.val) {

qNodeList = tmpQueue;

}

dfsNode(treeNode.left, p, q, tmpQueue);

dfsNode(treeNode.right, p, q, tmpQueue);

}

Queue<Integer> pList = new LinkedList<>();

Queue<Integer> qList = new LinkedList<>();

// implemented the int version

public int lowestCommonAncestorReturnInt(TreeNode root, TreeNode p, TreeNode q) {

int result = root.val;

dfsValue(root, p.val, q.val, new LinkedList<Integer>());

while (!pList.isEmpty()) {

int tmp = pList.poll();

// System.out.println(tmp);

if (tmp != qList.poll()) {

break;

}

result = tmp;

}

return result;

}

public void dfsValue(TreeNode treeNode, int p, int q, Queue<Integer> queue) {

if (null == treeNode)

return;

Queue<Integer> tmpQueue = new LinkedList<>();

tmpQueue.addAll(queue);

tmpQueue.add(treeNode.val);

if (treeNode.val == p) {

pList = tmpQueue;

}

if (treeNode.val == q) {

qList = tmpQueue;

}

dfsValue(treeNode.left, p, q, tmpQueue);

dfsValue(treeNode.right, p, q, tmpQueue);

}

public static void main(String[] args) {

TreeNode treeNode1 = new TreeNode(1);

TreeNode treeNode2 = new TreeNode(2);

TreeNode treeNode3 = new TreeNode(3);

TreeNode treeNode4 = new TreeNode(4);

TreeNode treeNode5 = new TreeNode(5);

TreeNode treeNode6 = new TreeNode(6);

TreeNode treeNode7 = new TreeNode(7);

treeNode1.left = treeNode2;

treeNode2.left = treeNode4;

treeNode2.right = treeNode5;

treeNode5.right = treeNode3;

treeNode3.left = treeNode6;

treeNode3.right = treeNode7;

LowestCommonAncestorOfABinaryTree lowestCommonAncestorOfABinaryTree = new LowestCommonAncestorOfABinaryTree();

lowestCommonAncestorOfABinaryTree.dfsValue(treeNode1, 7, 6, new LinkedList<Integer>());

for (int i : lowestCommonAncestorOfABinaryTree.pList) {

System.out.print(i + "*");

}

System.out.println();

for (int i : lowestCommonAncestorOfABinaryTree.qList) {

System.out.print(i + "-");

}

System.out.println();

System.out.println("result: " + lowestCommonAncestorOfABinaryTree.lowestCommonAncestorReturnInt(treeNode1, treeNode7, treeNode6));

}

algorithm/Week_02/id_26/Leetcode_236_26.java at master · feixiangcode/algorithm · GitHub

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