leetcode No236. Lowest Common Ancestor of a Binary Tree

Question

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).”

求二叉树最近公共祖先（LCA）

Algorithm

从下层开始往上，如果找到p或q就上传给父节点，假设left和right都找到了，则root就是最近公共祖先。如果根节点等于p或q，则根节点就是最近公共祖先（说明p是q的祖先或者q是p的祖先）。

Accepted Code

class Solution {public:    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {        if(root==NULL || root==p || root==q)            return root;        TreeNode* left=lowestCommonAncestor(root->left,p,q);        TreeNode* right=lowestCommonAncestor(root->right,p,q);        if(left!=NULL && right!=NULL)            return root;        return left==NULL?right:left;    }};