98. 验证二叉搜索树

原题

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

思路

递归

复杂度

时间：O(n)
空间：O(n)

Python代码

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def isValidBST(self, root: Optional[TreeNode]) -> bool:
        def isBST(root, left = float('-inf'), right = float('inf')):
            if not root:
                return True 
            if left >= root.val or right <= root.val:
                return False 
            if not isBST(root.left, left, root.val):
                return False 
            if not isBST(root.right, root.val, right):
                return False 
            return True 

        return isBST(root)

Go代码

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func isValidBST(root *TreeNode) bool {
	// 匿名函数
	var isBST func(*TreeNode, int, int) bool
	isBST = func(root *TreeNode, left int, right int) bool {
		if root == nil {
			return true
		}
		if left >= root.Val || right <= root.Val {
			return false
		}
		if isBST(root.Left, left, root.Val) == false {
			return false
		}
		if isBST(root.Right, root.Val, right) == false {
			return false
		}
		return true
	}
	return isBST(root, math.MinInt32-1, math.MaxInt32+1)
}