Share my C++ solution, easy to understand

  • 0
    class Solution {
        TreeNode* pre = NULL;
        bool isValidBST(TreeNode* root) {
            return is_valid(root);
        bool is_valid(TreeNode* root)
            if (root == NULL)
                return true;
            if (!is_valid(root->left))
                return false;
            if (pre != NULL && root->val <= pre->val)
                return false;
            pre = root;
            return is_valid(root->right);

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