剑指 Offer 68 - II. 二叉树的最近公共祖先

题目链接：https://leetcode.cn/problems/er-cha-shu-de-zui-jin-gong-gong-zu-xian-lcof/description/?favorite=xb9nqhhg

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:
map<TreeNode*,int>vis;
map<TreeNode*,TreeNode*>fa;
    void dfs(TreeNode *root)
    {
        if(root==NULL)
        {
            return ;
        }

        if(root->right!=NULL)
        {
            fa[root->right]=root;
            dfs(root->right);
        }
        if(root->left!=NULL)
        {
            fa[root->left]=root;
            dfs(root->left);
        }
    }
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        dfs(root);
        TreeNode *ans;
        while(p!=NULL)
        {
            vis[p]=1;
            p=fa[p];
        }
        while(q!=NULL)
        {
            if(vis[q]!=0)
            {
                //printf("%d\n",q->val);
                ans=q;
                break;
            }
            q=fa[q];
        }
        return ans;
    }
};