Java金字塔/三角形使用for循环

Question

i want to print a triangle/pyramid style like:

   1
  323
 54345
7654567

here is my code:

int lines = 5;

    for (int i = 1; i < lines; i++) {

        for (int j = 1; j < lines-i; j++) { 
            System.out.print(" ");
        }

        for (int j = i; j > 1; j--) { //this for loop is my problem. any solution?
            System.out.print(j);
        }

        for (int j = i; j < i+i; j++) { 
            System.out.print(j);
        }
        System.out.println();
}

what i got is

   1
  223
 32345
4324567

i been studying codes while working at office and i think week long i still could not find a solution to this even i use search in Google. i am only into enhancing my logic through conditionals and no heavy object oriented or recursion yet.

Answer 1

The problem in your first loop is a problem you figured out in your second one! (and it has something to do with the largest number in the loop)

for (int j = i; j > 1; j--) { //this for loop is my problem. any solution?
    System.out.print(j);
}

Look at the numbers on the left of the pyramid. They start where the ones on the right end (every line of the pyramid is symmetrical). And the general formula for that number is i + i - 1 , where i is the line number from your outer loop.

The second row starts at 2 * i - 1 = 2 * 2 - 1 = 3 . The third row starts at 2 * 3 - 1 = 5 etc.

Your second inner loop should therefore look like this:

for (int j = i + i - 1; j > i; j--) {
    System.out.print(j);
}

Answer 2

Here is the complete fixed source.

You have to start at the i-th odd number. This is i*2-1 . And you stop at i . This also fixes a spacing difference introduced by changing it to lines = 4 .

int lines = 4;

for (int i = 1; i <= lines; i++) {

    for (int j = 1; j < lines-i+1; j++) { 
        System.out.print(" ");
    }

    for (int j = i*2-1; j > i; j--) { //this for loop is my problem. any solution?
        System.out.print(j);
    }

    for (int j = i; j < i+i; j++) { 
        System.out.print(j);
    }
    System.out.println();
}

Run it here: http://ideone.com/AKsc1f

Answer 3

int lines = 4;

for (int i = 1; i <= lines; i++) {

for (int j = 1; j < lines-i+1; j++) { 
    System.out.print(" ");
}
//replace this
for(int j=0; j<i-1; j++) System.out.print(i*2-j-1);
 System.out.print(i);
 for(int j=; j<i-1;j++) System.out.print(i+j+1);
//==========
System.out.println();

}