LeetCode 5338. 二叉树中的最长交错路径(dfs)

/**
 * 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:
    int ans;
    void dfs(TreeNode *r,bool f, int cnt){
        if(r == NULL) return ;
        ans = max(ans, cnt);
        if(r->right) dfs(r->right, 1, f == 1 ? 1 : cnt + 1);
        if(r->left) dfs(r->left, 0, f == 0 ? 1 : cnt + 1);
        return ;
    }
    int longestZigZag(TreeNode* root) {
        ans = 0;
        if(root->left) dfs(root->left, 0, 1);
        if(root->right) dfs(root->right, 1, 1);
        return ans;
    }
};