标签：comm 左右 can turn between div bin 结果 its
来源：https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree
Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.
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).”
_______3______
/ ___5__ ___1__
/ \ / 6 _2 0 8
/ 7 4
For example, the lowest common ancestor (LCA) of nodes 5 and 1 is 3. Another example is LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.
递归搜索，当root非空时，对其左右两子数分别进行搜索。若搜索结果都为非空，则两个节点分别位于左右两个子树中，LCA为root节点；若其中一个结果为空，则另一个不为空的为LCA；若两个结果都为空，则返回null
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */ 10 class Solution { 11 public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { 12 if(root == null || (p == null && q == null)) { 13 return null; 14 } 15 if(root == p || root == q) { 16 return root; 17 } 18 TreeNode left = lowestCommonAncestor(root.left, p, q); 19 TreeNode right = lowestCommonAncestor(root.right, p, q); 20 if(left != null && right != null) { 21 return root; 22 } else if(left != null && right == null) { 23 return left; 24 } else if(left == null && right != null) { 25 return right; 26 } else { 27 return null; 28 } 29 } 30 }
Lowest Common Ancestor of a Binary Tree（二叉树公共祖先）
标签：comm 左右 can turn between div bin 结果 its
原文地址：http://www.cnblogs.com/renzongxian/p/7512246.html
