valid_bst
valid_bst.go 源码
package main
import (
"math"
"reflect"
"sort"
)
//验证二叉搜索树
//根据二叉搜索树的特性，进行递归判断
func isValidBST(root *TreeNode) bool {
return validBstHelper(root, math.MinInt64, math.MaxInt64)
}
func validBstHelper(node *TreeNode, lower, upper int) bool {
if node == nil {
return true
}
if node.Val <= lower || node.Val >= upper {
return false
}
return validBstHelper(node.Left, lower, node.Val) && validBstHelper(node.Right, node.Val, upper)
}
//中序遍历二叉树，然后看是否有序
func isValidBST2(root *TreeNode) bool {
if root == nil {
return true
}
set := map[int]bool{}
var temp []int
iterative(root, set, &temp)
var data []int
for v := range set {
data = append(data, v)
}
sort.Ints(data)
return reflect.DeepEqual(temp, data)
}
func iterative(node *TreeNode, data map[int]bool, temp *[]int) {
if node != nil {
iterative(node.Left, data, temp)
data[node.Val] = true
*temp = append(*temp, node.Val)
iterative(node.Right, data, temp)
}
}
//中序遍历优化，不用全部将结果保存，只需要每次比较前后节点的值即可
func isValidBST3(root *TreeNode) bool {
var stack []*TreeNode
var prev *TreeNode
cur := root
for cur != nil || len(stack) > 0 {
for cur != nil {
stack = append(stack, cur)
cur = cur.Left
}
node := stack[len(stack)-1]
stack = stack[:len(stack)-1]
if prev != nil && prev.Val >= node.Val {
return false
}
prev = node
cur = node.Right
}
return true
}
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