LeetCode236: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.

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public://采用先序遍历的方式    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&&right)//两个输入节点分别在root节点的不同子树中                return root;            else            {                return left?left:right;            }    }    };