week2 attempt 3

Author: BaeKwangho

validate-binary-search-tree/Baekwangho.ts

@@ -0,0 +1,90 @@
+/**
+ * Definition for a binary tree node.
+ * 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)
+ *     }
+ * }
+ */
+
+/**
+ 1차 시도
+
+function isValidBST(root: TreeNode | null): boolean {
+  let result = true;
+
+  function validate(node: TreeNode) {
+    if (node.left) {
+      if (node.val > node.left.val) {
+        validate(node.left);
+      } else {
+        result = false;
+      }
+    }
+
+    if (node.right) {
+      if (node.val < node.right.val) {
+        validate(node.right);
+      } else {
+        result = false;
+      }
+    }
+  }
+
+  validate(root);
+  return result;
+}
+  */
+
+interface TreeNode {
+  val: number;
+  left: TreeNode;
+  right: TreeNode;
+}
+
+/** 2차 시도 실패 */
+function isValidBST(root: TreeNode | null): boolean {
+  let result = true;
+
+  function validate(node: TreeNode, lstandard?: number, rstandard?: number) {
+    if (node.left) {
+      if (lstandard !== undefined && lstandard > node.left.val) {
+        result = false;
+      }
+
+      if (rstandard !== undefined && rstandard < node.left.val) {
+        result = false;
+      }
+
+      if (node.val > node.left.val) {
+        validate(node.left, undefined, node.val);
+      } else {
+        result = false;
+      }
+    }
+
+    if (node.right) {
+      if (lstandard !== undefined && lstandard > node.right.val) {
+        result = false;
+      }
+
+      if (rstandard !== undefined && rstandard < node.right.val) {
+        result = false;
+      }
+
+      if (node.val < node.right.val) {
+        validate(node.right, node.val, undefined);
+      } else {
+        result = false;
+      }
+    }
+  }
+
+  validate(root!);
+  return result;
+}