Question

I want to create a loop in Java that mathematically takes a variable, say one million, then reduces it by the steps detailed in the program & table below.

package com.sbs.test.maths;

import org.testng.annotations.Test;

public class Maths {
  @Test
  public void test() {
    int i = 1000000;
    System.out.println( i );
    while( i > 1 ) {
      i = reduce( i );
      System.out.println( i );
    }
  }

  private int reduce( int value ) {
    if ( value > 1 && value <= 10 ) value -= 1;
    else if ( value > 10 && value <= 100 ) value -= 10;
    else if ( value > 100 && value <= 1000 ) value -= 100;
    else if ( value > 1000 && value <= 10000 ) value -= 1000;
    else if ( value > 10000 && value <= 100000 ) value -= 10000;
    else if ( value > 100000 && value <= 1000000 ) value -= 100000; 
    else if ( value > 1000000 && value <= 10000000 ) value -= 1000000; 
    else if ( value > 10000000 && value <= 100000000 ) value -= 10000000; 
    return value;
  }
}

i.e.

value     reduce-by   result
1000000 - 100000    = 900000
900000  - 100000    = 800000
...
200000  - 100000    = 100000
100000  - 10000     = 90000
90000   - 10000     = 80000
...
20000   - 10000     = 10000
10000   - 1000      = 9000
9000    - 1000      = 8000
...
2000    - 1000      = 1000
1000    - 100       = 900
900     - 100       = 800
...
200     - 100       = 100
100     - 10        = 90
90      - 10        = 80

Can this be done without a nasty if cascade for detecting if the number is 100, 1000, 10000, 100000 or more?

I found a javascript example that I almost got to work in Java, but it wasn’t working for all variations. I ran the program below, but as you will see, it gets stuck at the point where we need to lose a zero on the end of the reduction.

System.out.println( "----------------------------------------------" );
for ( int i = 1000000; i > 0; i -= (int) Math.pow( 10, Math.floor( Math.log( i ) / Math.log(10) ) ) ) {
  System.out.println( i );
}

The output:

1000000
900000
800000
700000
600000
500000
400000
300000
200000
100000

Unfortunately maths is not my strong point, so any help on this is much appreciated.

Thanks!

Answer 1

    int total = 1000000;
    int reducedBy = 100000;
    while (total > 0 && reducedBy >= 1) {
        System.out.println(total);
        total -= reducedBy;
        if (total == reducedBy)
            reducedBy /= 10;
    }
    System.out.println(total);

In case you still need it.