如何使用Java反向打印图案

Question

I write a code that If num = 8 should show a output as below, but the code do not show that result, could any one help whats my wrong?

System.out.printf("Enter number of row for pattern to show : ");
            int num = input.nextInt();

    for(i=num-1;i>0;i--){
        for(j=1;j<=i;j++){
            if((i+j)%2==0)
                System.out.print(0);
            else
                System.out.print(1);
        }
        System.out.println();
        }

Expected output :

10101010
010101
01010
1010
010
10
0

Answer 1

There were a few issues with your code preventing it compiling

• You need to declare i and j in the for loops.
• Need convert String num to integer, via Integer.parseInt(num)
• -1 is unnecessary in the first for loop (unless you change the continuation condition to i >= 0 instead of i > 0 )

Fixing these...

for (int i = Integer.parseInt(num); i > 0; i--) {
    for (int j = 1; j <= i; j++) {
        if ((i + j) % 2 == 0) {
            System.out.print(0);
        } else {
            System.out.print(1);
        }
    }
    System.out.println();
}

This gives a slightly different output, ie the original question does not output a line of length 7, it goes from 8 to 6. Also line 6 is 'off by one' This is almost certainly a typo in the original question.

Original question        My output

1) 10101010              10101010
2) <= missing =>         0101010
3) 010101                101010     <== mismatch. expected ends in 1
4) 01010                 01010
5) 1010                  1010
6) 010                   010
7) 10                    10
8) 0                     0

This can be worked around

for (int i = Integer.parseInt(num); i > 0; i--) {
    if (i == 7) {
        continue; // conform to broken question
    }
    if (i == 6) {
        System.out.println("010101"); // conform to broken question
        continue;
    }
    ...

Which now gives the expected output

10101010
010101
01010
1010
010
10
0

Answer 2

I made a couple changes to your code, and commented what they were. I...

1. declared Scanner method called input

2. made num of type int (rather than String )

3. Declared i and j in your for loops

4. fixed the first for loop(used to be i=num-1 , should be i=num ).

Code shown below:

Scanner input = new Scanner(System.in); //created Scanner method
        System.out.printf("Enter number of row for pattern to show : ");
        int num = input.nextInt(); //num should be of type 'int', not String

        for(int i=num; i>0; i--) { //Declared 'i', 'i' should equal 'num', not 'num-1'
            for(int j=1; j<=i; j++) { //Declared 'j'
                if((i+j)%2==0)
                    System.out.print(0);
                else
                    System.out.print(1);
            }
            System.out.println();
        }

And when num is 8, you get the output you desired:

Enter number of row for pattern to show : 8
10101010
0101010
101010
01010
1010
010
10
0