u

2026-06-22 20:50:10 +10:00
parent b63ad2d95d
commit 5c25a2e856
7 changed files with 218 additions and 0 deletions
@@ -0,0 +1,66 @@
+package top100liked
+
+// https://leetcode.cn/problems/validate-binary-search-tree/description/?envType=study-plan-v2&envId=top-100-liked
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+// AC, 但很慢
+// func inorderTraversal(root *TreeNode) []int {
+// 	if root == nil {
+// 		return []int{}
+// 	}
+// 	res := []int{}
+// 	if root.Left != nil {
+// 		res = append(res, inorderTraversal(root.Left)...)
+// 	}
+// 	res = append(res, root.Val)
+// 	if root.Right != nil {
+// 		res = append(res, inorderTraversal(root.Right)...)
+// 	}
+// 	return res
+// }
+
+// func isValidBST(root *TreeNode) bool {
+// 	if root == nil {
+// 		return true
+// 	}
+// 	l := inorderTraversal(root)
+// 	if len(l) == 1 {
+// 		return true
+// 	}
+// 	for i, j := 0, 1; j < len(l); {
+// 		if l[i] >= l[j] {
+// 			return false
+// 		}
+
+// 		i++
+// 		j++
+// 	}
+// 	return true
+// }
+
+func isValidBST(root *TreeNode) bool {
+	var prev *int
+	var inorder func(node *TreeNode) bool
+	inorder = func(node *TreeNode) bool {
+		if node == nil {
+			return true
+		}
+		if !inorder(node.Left) {
+			return false
+		}
+		if prev != nil && *prev >= node.Val {
+			return false
+		}
+		prev = &node.Val
+		if !inorder(node.Right) {
+			return false
+		}
+		return true
+	}
+	return inorder(root)
+}