Day03Homework

/**
 * d打印九九乘法表
 */
public class Test01 {
    public static void main(String[] args) {
        for (int i =1; i <=9 ; i++) {
            for (int j =1; j <=i ; j++) {
                System.out.print(j+"×"+i+"="+i*j+" ");
            }
            System.out.println();
        }
    }
}
/*输出结果
1×1=1 
1×2=2 2×2=4 
1×3=3 2×3=6 3×3=9 
1×4=4 2×4=8 3×4=12 4×4=16 
1×5=5 2×5=10 3×5=15 4×5=20 5×5=25 
1×6=6 2×6=12 3×6=18 4×6=24 5×6=30 6×6=36 
1×7=7 2×7=14 3×7=21 4×7=28 5×7=35 6×7=42 7×7=49 
1×8=8 2×8=16 3×8=24 4×8=32 5×8=40 6×8=48 7×8=56 8×8=64 
1×9=9 2×9=18 3×9=27 4×9=36 5×9=45 6×9=54 7×9=63 8×9=72 9×9=81 
*/

/**
 * 求矩阵对角线元素之和
 */
public class Test02 {
    public static void main(String[] args) {
        int[][] arr = {
                {1,2,3,4,5},
                {1,2,3,4,5},
                {1,2,3,4,5},
                {1,2,3,4,5},
                {1,2,3,4,5},
        };
        int sum = 0;
        for (int i = 0; i <arr.length ; i++) {
            for (int j = 0; j <arr[i].length ; j++) {
                if (i==j || i+j==arr.length-1){
                    sum += arr[i][j];
                }
            }
        }
        System.out.println(sum);
    }
}
/*
    输出结果  27

 */

/**
 * 打印杨辉三角
 */
public class Test03 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输出你要打印的行数");
        int n = scanner.nextInt();
        int arr[][] = new int[n][];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = new int[i + 1];
            for (int j = 0; j < arr[i].length; j++) {
                arr[i][0] = 1;
                arr[i][arr[i].length - 1] = 1;
            }
        }
        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];
            }
        }
        for (int i = 0; i <arr.length ; i++) {
            for (int j = 0; j <arr[i].length ; j++) {
                System.out.print(arr[i][j]+" ");
            }
            System.out.println();
        }
    }
}
/**
 * 输出结果
 *请输出你要打印的行数
 * 10
 * 1
 * 1 1
 * 1 2 1
 * 1 3 3 1
 * 1 4 6 4 1
 * 1 5 10 10 5 1
 * 1 6 15 20 15 6 1
 * 1 7 21 35 35 21 7 1
 * 1 8 28 56 70 56 28 8 1
 * 1 9 36 84 126 126 84 36 9 1
 */