CODEWITHSUNDEEP
javaarraysfor-loop
kiko
kiko

Reputation: 23

Java: Eliminating results with same numbers

Ok, I stripped this code as much as I could. The solution I'm seeking is probably simple. Here it goes:

import java.util.Arrays;

public class App {
    public static void main(String[] args) {
        for (int k = 1; k < 9; k++) {
            for (int p = 1; p < 9; p++) {
                for (int i = 1; i < 9; i++) {
                    if (k + p + i == 9) {
                        System.out.println("The 3 numbers that give the sum of 9 are: " + k + p + i);
                    }
                }
            }
        }
    }
}

I'm trying to find all combinations of 3 numbers that sum up to number 9. I've done this through 3 for loops as you can see in the code but the problem is that the result also displays same numbers but in different order. For example: 117 and 711. I don't want that, I just want one combination of the same numbers. What is the simplest solution to this?

Upvotes: 1

Views: 50

Answers (3)

Luigi Cortese
Luigi Cortese

Reputation: 11131

As someone else already said, one possible right answer is 

    for (int k = 1; k < 9; k++) 
        for (int p = k + 1; p < 9; p++) 
            for (int i = p + 1; i < 9; i++) 
                if (k + p + i == 9)
                    System.out.println(""+k + p + i);

But do you really understand why?

Imagine you're looking for combinations of 2 numbers that sum up to 9. You could use just two index, say k and p, and imagine your set of couples as points on a 2D plane

enter image description here

You can easily spot the points you're interested in, the ones that sums up to 9, here represented as blue dots:

enter image description here

Here you have exactly 10 possible solutions to your [semplified] problem (0,9), (1,8), (2,7), (3,6), (4,5), (5,4), (6,3), (7,2), (8,1), (9,0), and every solution has a twin solution you want to get rid of.

How can you do that? By declaring int p = k + 1. This, from the point of view of our plane, means excluding half of the portion of possible solutions from your search:

enter image description here

cutting off the red area and, consequentely, duplicate solutions. Hence, the solution for the simplified problem would be (including 0 and 9)

    for (int k = 0; k <= 9; k++) 
        for (int p = k + 1; p <= 9; p++) 
            if (k + p == 9)
                System.out.println(""+k + p);

and the output would be 

09
18
27
36
45

Upvotes: 1

Orel Eraki
Orel Eraki

Reputation: 12196

Then you should limit your inner loops.

Solution: p < 9 should be p <= k and i < 9 should be i <= p

Code:

public static void main(String[] args) {
    for (int k = 1; k < 9; k++) {
        for (int p = 1; p <= k; p++) {
            for (int i = 1; i <= p; i++) {
                if (k + p + i == 9) {
                    System.out.println("The 3 numbers that give the sum of 9 are: " + k + p + i);

                }

            }
        }
    }
}

Upvotes: 2

Shrinivas Shukla
Shrinivas Shukla

Reputation: 4453

Change your main method to this..

for (int k = 1; k < 9; k++) {
    for (int p = k + 1; p < 9; p++) {
        for (int i = p + 1; i < 9; i++) {

            if (k + p + i == 9) {
                System.out.println("The 3 numbers that give the sum of 9 are: " + k + p + i);

            }

        }
    }
}

Upvotes: 0

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