规范格式

leetcode/0098.Validate-Binary-Search-Tree/98. Validate Binary Search Tree.go

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+package leetcode
+
+import "math"
+
+import (
+	"github.com/halfrost/LeetCode-Go/structures"
+)
+
+// TreeNode define
+type TreeNode = structures.TreeNode
+
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+
+// 解法一，直接按照定义比较大小，比 root 节点小的都在左边，比 root 节点大的都在右边
+func isValidBST(root *TreeNode) bool {
+	return isValidbst(root, math.Inf(-1), math.Inf(1))
+}
+func isValidbst(root *TreeNode, min, max float64) bool {
+	if root == nil {
+		return true
+	}
+	v := float64(root.Val)
+	return v < max && v > min && isValidbst(root.Left, min, v) && isValidbst(root.Right, v, max)
+}
+
+// 解法二，把 BST 按照左中右的顺序输出到数组中，如果是 BST，则数组中的数字是从小到大有序的，如果出现逆序就不是 BST
+func isValidBST1(root *TreeNode) bool {
+	arr := []int{}
+	inOrder(root, &arr)
+	for i := 1; i < len(arr); i++ {
+		if arr[i-1] >= arr[i] {
+			return false
+		}
+	}
+	return true
+}
+
+func inOrder(root *TreeNode, arr *[]int) {
+	if root == nil {
+		return
+	}
+	inOrder(root.Left, arr)
+	*arr = append(*arr, root.Val)
+	inOrder(root.Right, arr)
+}

leetcode/0098.Validate-Binary-Search-Tree/98. Validate Binary Search Tree_test.go

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+package leetcode
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/halfrost/LeetCode-Go/structures"
+)
+
+type question98 struct {
+	para98
+	ans98
+}
+
+// para 是参数
+// one 代表第一个参数
+type para98 struct {
+	one []int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans98 struct {
+	one bool
+}
+
+func Test_Problem98(t *testing.T) {
+
+	qs := []question98{
+
+		question98{
+			para98{[]int{10, 5, 15, structures.NULL, structures.NULL, 6, 20}},
+			ans98{false},
+		},
+
+		question98{
+			para98{[]int{}},
+			ans98{true},
+		},
+
+		question98{
+			para98{[]int{2, 1, 3}},
+			ans98{true},
+		},
+
+		question98{
+			para98{[]int{5, 1, 4, structures.NULL, structures.NULL, 3, 6}},
+			ans98{false},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 98------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans98, q.para98
+		fmt.Printf("【input】:%v      ", p)
+		rootOne := structures.Ints2TreeNode(p.one)
+		fmt.Printf("【output】:%v      \n", isValidBST(rootOne))
+	}
+	fmt.Printf("\n\n\n")
+}

leetcode/0098.Validate-Binary-Search-Tree/README.md

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+# [98. Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/)
+
+
+## 题目
+
+Given a binary tree, determine if it is a valid binary search tree (BST).
+
+Assume a BST is defined as follows:
+
+- The left subtree of a node contains only nodes with keys **less than** the node's key.
+- The right subtree of a node contains only nodes with keys **greater than** the node's key.
+- Both the left and right subtrees must also be binary search trees.
+
+**xample 1:**
+
+        2
+       / \
+      1   3
+    
+    Input: [2,1,3]
+    Output: true
+
+**Example 2:**
+
+        5
+       / \
+      1   4
+         / \
+        3   6
+    
+    Input: [5,1,4,null,null,3,6]
+    Output: false
+    Explanation: The root node's value is 5 but its right child's value is 4.
+
+## 题目大意
+
+给定一个二叉树，判断其是否是一个有效的二叉搜索树。假设一个二叉搜索树具有如下特征：
+
+- 节点的左子树只包含小于当前节点的数。
+- 节点的右子树只包含大于当前节点的数。
+- 所有左子树和右子树自身必须也是二叉搜索树。
+
+
+## 解题思路
+
+- 判断一个树是否是 BST，按照定义递归判断即可