一 遍历杨辉三角左半部分（此方法运行到10000时提示越界，通过率73%）

import java.util.*;

public class YangHui {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[][] arr = new int[n][];
        for(int i = 0; i < arr.length; i++){
            arr[i] = new int[i+1];
            arr[i][0] = 1;
            for (int j = 1; j < arr[i].length; j++) {
                if(i <= 1){
                    arr[i][j] = 1;
                } else {
                    if(j == 1){
                        arr[i][j] = arr[i-1][j-1] + arr[i-1][j];
                    }
                    else if(j == arr[i].length - 1){
                        arr[i][j] = (arr[i-1][j-2] * 2) + arr[i-1][j-1];
                    }
                    else{
                        arr[i][j] = arr[i-1][j-2] + arr[i-1][j-1] + arr[i-1][j];
                    }
                }
            }
        }
        int index = -1;
        for (int j = 0; j < n ; j++) {
            if (arr[n - 1][j] % 2 == 0){
                index = j + 1;
                break;
            }
        }
        System.out.println(index);
    }
}

二 找规律（通过100%）

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
    /*
 1-  0            1
 2-  0            1 1
 3-  2            1 2 3
 4-  3            1 3 6 7
 5-  2            1 4 10 16 19
 6-  4            1 5 15 30 45 51
 7-  2            1 6 21 50 90 126 141
 8-  3            1 7 28 77 161 266 357 393
 9-  2            1 8 36 112 266 504 784 1016 1107
 10- 4            1 9 45 156 414 882 1554 2304 2907 3139
 
规律：
刨去前两行，每4行一个轮回，位数2,3,2,4循环；
     */
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int index = -1;
        if(n > 2){
            if((n-2) % 4 == 1 || (n-2) % 4 == 3){
                index = 2;
            }
            else if((n-2) % 4 == 2){
                index = 3;
            }
            else if((n-2) % 4 == 0){
                index = 4;
            }
        }
        System.out.println(index);
    }
}