98. Validate Binary Search Tree

leetcode.com/problems/validate-binary-search-tree/

Validate Binary Search Tree - LeetCode

class Solution {
    public boolean isValidBST(TreeNode root) {
        return isValidBST(root, false, false, 0, 0);
    }
    
    public boolean isValidBST(TreeNode root, boolean isLower, boolean isUpper, int lower, int upper) {
        if(root == null) return true;
        // 현재 노두가 lower/upper 를 침범하지 않는가
        if(isLower && root.val <= lower) {
            return false;
        }
        if(isUpper && root.val >= upper) {
            return false;
        }
        
        return isValidBST(root.left, isLower, true, lower, root.val)
            && isValidBST(root.right, true, isUpper, root.val, upper);
    }
}

 

leetcode.com/problems/validate-binary-search-tree/discuss/32112/Learn-one-iterative-inorder-traversal-apply-it-to-multiple-tree-questions-(Java-Solution)

Learn one iterative inorder traversal, apply it to multiple tree questions (Java Solution) - LeetCode Discuss