leetcode 236. 二叉树的最近公共祖先

 

代码：

/**
 * 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:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if (root== NULL)
        {
            return NULL;
        }
        if(root == p || root ==q)
        {
            return root;
        }
        TreeNode * left = lowestCommonAncestor(root->left,p,q);
        TreeNode* right = lowestCommonAncestor(root->right,p,q);
        if(left==NULL)
        {
            return right;
        }
        if(right == NULL)
        {
            return left;
        }
        if(left&&right)//P 和q 在两侧
        {
            return root;
        }
        return NULL;
    }
};