[LeetCode]235. Lowest Common Ancestor of a Binary Search Tree

Problem Description

Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.

According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself).”

[]https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/]

思路

没看清题目，没注意是BST，所以写了个一般二叉树的。。

具体思路请看[]http://blog.csdn.net/u012468264/article/details/50817712]

Code

package q236;

import java.util.*;

import TreeNode.*;

public class Solution {

public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
List<List<TreeNode>> path = new ArrayList<List<TreeNode>>();
List<TreeNode> tmp = new ArrayList<TreeNode>();
tmp.add(root);
helper(tmp, root, p, path);
helper(tmp, root, q, path);
for (int i = path.get(0).size() - 1; i >= 0; i--) {
for (int j = path.get(1).size() - 1; j >= 0; j--) {
if (path.get(0).get(i) == path.get(1).get(j))
return path.get(0).get(i);
}
}
return null;

}

public void helper(List<TreeNode> path, TreeNode root, TreeNode target,
List<List<TreeNode>> ans) {
if (root == target) {
ans.add(new ArrayList<TreeNode>(path));
return;
} else {
if (root.left != null) {
path.add(root.left);
helper(path, root.left, target, ans);
path.remove(path.size() - 1);
}
if (root.right != null) {
path.add(root.right);
helper(path, root.right, target, ans);
path.remove(path.size() - 1);
}

}

}

// public static void main(String[] args) {
// Solution s = new Solution();
// Codec c = new Codec();
// TreeNode root = c
// .deserialize("6,2,8,0,4,7,9,null,null,3,5,null,null,null,null");
// TreeNode p = c.getNode(root, 2);
// TreeNode q = c.getNode(root, 8);
// // System.out.println(p.val);
// // System.out.println(q.val);
// TreeNode ans = s.lowestCommonAncestor(root, p, q);
// System.out.println(ans.val);
//
// }
}