AC https://leetcode-cn.com/problems/validate-binary-search-tree/

Author: AaronLinRC

src/main/kotlin/leetcode/validate-binary-search-tree/Solution.kt

@@ -0,0 +1,49 @@
+package leetcode.`validate-binary-search-tree`
+
+import TreeNode
+import org.junit.Test
+
+class Solution {
+    fun isValidBST(root: TreeNode?): Boolean {
+        return process(root)!!.isBST
+    }
+
+    private fun process(node: TreeNode?): ReturnType? {
+        if (node == null) return null
+
+        val left = process(node.left)
+        val right = process(node.right)
+
+        var min: Int = node.`val`
+        var max: Int = node.`val`
+        var isBST = true
+        if (left != null) {
+            min = Math.min(left.min, node.`val`)
+            max = Math.max(left.max, node.`val`)
+            isBST = left.isBST && node.`val` > left.max
+        }
+        if (right != null) {
+            min = Math.min(right.min, min)
+            max = Math.max(right.max, max)
+            isBST = isBST && right.isBST && node.`val` < right.min
+        }
+
+        return ReturnType(isBST, min, max)
+    }
+
+    class ReturnType(var isBST: Boolean, var min: Int, var max: Int)
+
+    @Test
+    fun test(){
+        val node1 = TreeNode(5)
+        val node2 = TreeNode(4)
+        val node3 = TreeNode(6)
+        val node4 = TreeNode(3)
+        val node5 = TreeNode(7)
+        node1.left = node2
+        node1.right = node3
+        node3.left = node4
+        node3.right = node5
+        isValidBST(node1)
+    }
+}