在Java中打印数字的模式序列

Question

I need to write a method called printOnLines() that takes two arguments an integer n and an integer inLine and prints the n integer, every inLine on a line.

for n = 10, inLine = 3:
1, 2, 3
4, 5, 6
7, 8, 9
10

My call is (10,3) . Here's my code:

public static void printOnLines(int n, int s) {
        for(int i=1; i<=s; i++) {
            for(int j=1; j<=n-1; j++) {
                System.out.print(j + ", ");
            }
        System.out.println();
        }
    }
}

I believe that there are two mistakes:

1. I need to remove the last comma appearing in the output.
2. I need to place 3 of the numbers of each line until I reach the number 10.

Answer 1

Use this:

public static void printOnLines(int n, int s){
     StringBuilder builder = new StringBuilder();
     for(int i = 1; i <= n; i++){
         builder.append(i);
         if(i % s == 0)builder.append("\n");
         else builder.append(", ");
     }
     System.out.println(builder.toString().substring(0,builder.toString().length() - 2));
}

Answer 2

I'm not going to post a complete solution, since this is clearly homework. But here is what I would do, if I weren't allowed to use if statements or ternary operators.

• Make the index of the outer loop start at 0 and increase by s on every iteration, instead of by 1 (So it goes 0, 3, 6, 9 in your example).
• Print the sum of the two loop indexes on each iteration.
• Print the last number on each line outside of the inner loop, without a comma.

Edit

OK, on @localhost's request, here is my solution.

public static void printOnLines(int n, int s) {
    for (int i = 0; i < n; i += s) {
        int j;
        for (j = 1; j < s && i + j < n; j++) {
             System.out.print(i + j + ", ");
        }
        System.out.println(i + j);
    }
}

Answer 3

I assume you've already had to submit your homework, so here's how I'd do it:

class printonlines {
public static void main(String[] args) {        
    printOnLines(Integer.parseInt(args[0]),Integer.parseInt(args[1]));
}

public static void printOnLines(int n, int s) {     
    for(int i=1; i<=n; i++) {  // do this loop n times
        if ( (i != 1) && (i-1)%s == 0 ) {  // if i is exactly divisible by s, but not the first time
            System.out.println(); // print a new line
        }
        System.out.print(i);
        if (i != n) {  // don't print the comma on the last one
            System.out.print(", ");
        }
    }
    }
}

Oh, you don't want to use any if statements. All you really learn from doing "tricks" like what you are asked to do is a single trick, not how to write easily comprehensible (even by yourself when you have to debug later) code.

Anyway, here's my less comprehensible but more tricky code that doesn't use if as per the suggestions from the answer from @DavidWallace. I'm sure someone can do it neater but this is the best I could do in 15 minutes...

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

        printOnLines(Integer.parseInt(args[0]),Integer.parseInt(args[1]));
    }

    // i 012012012
    // j 000333666
  // i+j 012345678

    public static void printOnLines(int n, int s) {

        int i = 0;
        int j = 1;
        for (; j <= n; j+=s) {
            for (; i < (s-1) && (j+i)<n; i++) {

                 System.out.print((i+j) + ", ");
            }
            System.out.println(i+j);
            i=0;
        }
    }
}

Answer 4

Here is the code sample you wanted..

public static void printOnLines(int n, int s) {
    for (int i = 1; i < n; i++) {
        System.out.print(i + ",\t");
        if (i % 3 == 0) System.out.println();
    }
    System.out.println(n);
}