杨辉三角

package hnkjxy;

import java.util.Scanner;

public class yanghuisanjiao {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.println("输入杨辉三角的行数：");
        int n = input.nextInt();
        //二维数组定义
        int[][] arr = new int[n][];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = new int[i   + 1];//为第i行分配空间

        }

        //每一行的第一列和最后一列都是1
        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[i].length; j++) {
                arr[i][0] = 1;//每行第一列
                arr[i][j] = 1;//每一行最后一列

            }
        }
        //从第三行开始，元素=上一行本列元素+上一行前一列元素
        for (int i = 2; i < arr.length; i++) {
            for (int j = 1; j < arr[i].length - 1; j++) {
                arr[i][j] = arr[i - 1][j] + arr[i - 1][j - 1];
            }
        }
        //遍历输出二维数组
        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[i].length; j++) {
                System.out.print(arr[i][j] + "\t");
            }
            System.out.print("\n");
        }
    }
}