快手第一题

0.7 不知道是不是因为left写成了right

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

class TreeNode{
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x){
        val = x;
    }
}

public class Main{
    public static boolean check(TreeNode root){
        if(root == null) 
            return true;
        List<Integer> res = new ArrayList<>();
        inOrder(root, res);
        for(int i = 0; i < res.size()-1; i++){
            if(res.get(i) > res.get(i+1))
                return false;
        }
        return true;
    }
    
    private static void inOrder(TreeNode root,List<Integer> list){
        if(root == null) return ;
        inOrder(root.left, list);
        list.add(root.val);
        inOrder(root.right, list);
    }
    public static void main(String[] args){
        List<Integer> res = new ArrayList<>();
        Scanner cin = new Scanner(System.in);
        String val = cin.nextLine();
        String[] nums = val.split(",");
        for (int i = 0; i < nums.length; i++) {
            int v = Integer.parseInt(nums[i]);
            res.add(v);
        }
        TreeNode root = build(res, 0);
        
        if(check(root) == false)
            System.out.println("False");
        else
            System.out.println("True");
        
    }
    private static TreeNode build(List<Integer> a, int index) {
        TreeNode t = null;
        if(index < a.size()) {
            Integer val = a.get(index);
            if(val == null) {
                return null;
            }
            t = new TreeNode(val);
            t.left = build(a, 2*index+1);
            t.right = build(a, 2*index+2);
            return t;
        }
        return t;
    }
}