剑指offer树68-II.二叉树的最近公共祖先

Posted 2021-03-01 trevo

二叉树的最近公共祖先

/**
 * 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)   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 && right)   return root;
        return left ? left : right; // 只有一个非空则返回该指针，两个都为空则返回空指针
    }
};