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程式語言 - LeetCode - C++ - 98. Validate Binary Search Tree

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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:
    bool isValidBST(TreeNode* root) {
        auto dfs = [&](this auto&& dfs, TreeNode* n, long long lower, long long upper) -> bool {
            if (!n) {
                return true;
            }

            if (n->val <= lower || n->val >= upper) {
                return false;
            }

            return dfs(n->left, lower, n->val) && dfs(n->right, n->val, upper);
        };

        return dfs(root, LONG_MIN, LONG_MAX);
    }
};