Week 2

- validate-binary-search-tree

Author: jiji-hoon96

validate-binary-search-tree/jiji-hoon96.ts

@@ -0,0 +1,27 @@
+class TreeNode {
+	val: number;
+	left: TreeNode | null;
+	right: TreeNode | null;
+	constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+		this.val = val === undefined ? 0 : val;
+		this.left = left === undefined ? null : left;
+		this.right = right === undefined ? null : right;
+	}
+}
+
+function isValidBST(root: TreeNode | null): boolean {
+	function dfs(node: TreeNode | null, min: number, max: number) {
+		if (node === null) return true;
+
+		if (node.val <= min || node.val >= max) {
+			return false;
+		}
+
+		return dfs(node.left, min, node.val) && dfs(node.right, node.val, max);
+	}
+
+	return dfs(root, Number.NEGATIVE_INFINITY, Number.POSITIVE_INFINITY);
+}
+
+isValidBST([2, 1, 3]); // true
+isValidBST([5, 1, 4, null, null, 3, 6]); // false