程式語言 - LeetCode - C++ - 1372. Longest ZigZag Path in a Binary Tree

參考資訊：
https://www.cnblogs.com/cnoodle/p/17342376.html

題目：


解答：

/**
 * 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 longestZigZag(TreeNode* root) {
        return dfs(root, 0, 0);
    }

    int dfs(TreeNode *n, int cnt, int left) {
        int r = 0;

        if (!n) {
            return cnt;
        }

        if (left) {
            if (n->left) {
                r = max(dfs(n->left, cnt + 1, 0), r);
            }

            if (n->right) {
                r = max(dfs(n->right, 1, 1), r);
            }
        }
        else {
            if (n->right) {
                r = max(dfs(n->right, cnt + 1, 1), r);
            }

            if (n->left) {
                r = max(dfs(n->left, 1, 0), r);
            }
        }

        return max(cnt, r);
    }
};