0098-validate-binary-search-tree.ts

/**
 * Definition for a binary tree node.
 * class TreeNode {
 * val: number
 * left: TreeNode | null
 * right: TreeNode | null
 * constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 * this.val = (val===undefined ? 0 : val)
 * this.left = (left===undefined ? null : left)
 * this.right = (right===undefined ? null : right)
 * }
 * }
 */

functionisValidBST(root: TreeNode|null): boolean{
returnvalidate(root,null,null);
}

functionvalidate(
root: TreeNode|null,
max: number|null,
min: number|null
): boolean{
if(!root){
returntrue;
}

if(
(max!==null&&root.val>=max)||
(min!==null&&root.val<=min)
){
returnfalse;
}

return(
validate(root.left,root.val,min)&&
validate(root.right,max,root.val)
);
}