Reputation: 21

How do structure more than one for loop into an if statement?

I'm trying to solve a problem with an array of numbers and 3 for loops in Java. It involves figuring out which 3 numbers from the array add up to a specific sum. For this test I used a sum of 9.

int nums[] = {1, 3, 5, 7, 9, 11, 13, 15};

for (int i = 0; i <= 7; i++) {
    for (int j = 0; j <= 7; j++)
        for (int y = 0; y <= 7; y++)

            if(nums[i] + nums[j] + nums[y] == 9)
                System.out.print(i + " " + j + " " + y);
}

The correct answer is 3 3 3 but this output reads:

0 0 30 1 20 2 10 3 01 0 21 1 11 2 02 0 12 1 03 0 0

I know I'm probably nesting the for loops completely wrong but I can't figure out where to put the code blocks without getting rid of one of the variables in the scope of the if statement. Thanks for any help.

Upvotes: 1

Answers (3)

Devesh Kumar Singh

Reputation: 20490

Some issues in your code

You are printing the indexes System.out.print(i + " " + j + " " + y); instead you want to print the numbers.
You want to use println to print everything on a newline
You should not take a item from the list multiple times, every inner loop should ignore elements already taken in account by outer loop
3,3,3 is not the answer since it contains repeated elements, the answer should be the one which contains distinct elements i.e. 1,3,5

The updated code will then be

for (int i = 0; i <= 7; i++) {
    for (int j = i+1; j <= 7; j++)
        for (int y = j+1; y <= 7; y++)

            if( nums[i] + nums[j] + nums[y] == 9)
                //Print the numbers on newline
                System.out.println(nums[i] + " " +nums[j] + " " + nums[y]);
}

The output will be

1 3 5

If repetition is allowed, then all 3 loops will run from 0 and the answer changes

for (int i = 0; i <= 7; i++) {
    for (int j = 0; j <= 7; j++)
        for (int y = 0; y <= 7; y++)

            if( nums[i] + nums[j] + nums[y] == 9)
                //Print the numbers on newline
                System.out.println(nums[i] + " " +nums[j] + " " + nums[y]);
}

The answer will then be

Upvotes: 1

0liveradam8

Reputation: 778

You're testing the same values multiple times, i.e. 1+1+7, 1+7+1, 7+1+1 are all being tested. Use for for (int j = i; j <= 7; j++) and for (int y = j; y <= 7; y++). Note that there are multiple answers, not just 3 3 3, if you are allowing values to be used multiple times.

Upvotes: 0

Neeraj Jain

Reputation: 7730

The correct answer is 3 3 3 but this output reads:

No, The correct answer is definitely not 3 3 3, So if I am not wrong you want to find a triplet which sums up to your test sum, which in this case is 9, So correct answer is 1,3,5 Try this :

for (int i = 0; i <= 7; i++) {
  for (int j = i + 1; j <= 7; j++)
   for (int y = j + 1; y <= 7; y++)

      if (nums[i] + nums[j] + nums[y] == 9)
       System.out.print(nums[i] + " " + nums[j] + " " + nums[y]);
}

Running Sample : https://ideone.com/5UAuGv

Upvotes: 0

How do structure more than one for loop into an if statement?

Answers (3)

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