leetcode 236. 二叉树的最近公共祖先

https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-tree/

思路参考 剑指offer52题

class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        vector path_p;
        getPath(root, p, path_p);
        
        vector path_q;
        getPath(root, q, path_q);
        
        auto it_p = path_p.begin();
        auto it_q = path_q.begin();
        TreeNode *res = NULL;
        while(it_p != path_p.end() && it_q != path_q.end())
        {
            if (*it_p != *it_q)
                break;
            
            res = *it_q;            
            ++it_p;
            ++it_q;
        }
        
        return res;
    }
    
    bool getPath(TreeNode* root, TreeNode* t, vector &path)
    {
        if (root == NULL)
            return false;
        
        path.push_back(root);
        if (root==t)
        {
            return true;
        }            
        
        bool found = getPath(root->left, t, path) || getPath(root->right, t, path);
        if (!found)
        {
            path.pop_back();
        }
        
        return found;
    }
};

leetcode官方解答更好

class Solution {
public:
    TreeNode* ans;
    
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        ans = NULL;
        dfs(root,p,q);
        return ans;
    }
    
    int dfs(TreeNode* root, TreeNode* p, TreeNode* q)
    {
        if (root == NULL)
            return 0;
        
        int left = dfs(root->left, p, q);
        int right = dfs(root->right, p, q);
        int mid = (root == p || root == q);
            
        int sum = left+right+mid;
        if (sum>=2)
        {
            ans = root;
        }
        
        return !!sum;
    }
};