1372.longest-zig-zag-path-in-a-binary-tree.cpp

/*
 * @lc app=leetcode id=1372 lang=cpp
 *
 * [1372] Longest ZigZag Path in a Binary Tree
 */

// @lc code=start
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution
{
public:
    int dfs(TreeNode *root, int left, int cnt)
    {
        if (!root)
            return cnt;
        if(left)
            return max(dfs(root->right, 0, cnt + 1), dfs(root->left, 1, 0));
        return max(dfs(root->left, 1, cnt + 1), dfs(root->right, 0, 0));
    }
    int longestZigZag(TreeNode *root)
    {
        return max(dfs(root->left, 1, 0), dfs(root->right, 0, 0));
    }
};
// @lc code=end