Question

I have an array from ten (or more) numbers, for example:

arr[1,2,3,4,5,6,7,8,9,10]

I want a method to check if three numbers from this arrays have the same sum to another three numbers (I want to get all the possibilities!), for example:

{1.8.10}  {2.10.7}  {3.7.9}   {4.9.6}   {5.6.8}  {Sum of each set: 19}
{1.6.10}  {3.10.4}  {5.4.8}   {7.8.2}   {9.2.6}  {Sum of each set: 17}
{6.3.5}   {7.5.2}   {8.2.4}   {9.4.1}   {10.1.3} {Sum of each set: 14}

Update:

That’s another example to what exactly I want to do:

alt text http://img208.imageshack.us/img208/1131/77603708.png

Answer 1

Create a map of sets. Setup a triple nested for loop and start adding numbers. Every sum becomes a key into the map. The set is the 3 numbers you used. Should only be a dozen or so lines of code.

map&ltint,set&ltint> > sums;

for(int i=0; i&ltARRAY_SIZE; i++)
{
  for(int j=0; j&ltARRAY_SIZE; j++)
  {
    if(j &lt= i)
      continue;

    for(int k=0; k&ltARRAY_SIZE; k++)
    {
      if(k &lt= i || k &lt= j)
        continue;

      int localSum = arr[i] + arr[j] + arr[k];
      set&ltint> thisSum;
      thisSum.insert(arr[i]);
      thisSum.insert(arr[j]);
      thisSum.insert(arr[k]);
      sums.insert(make_pair(localSum, thisSum));
    }
  }
}

and just iterate through the sums map and display your sets as you want. I’m not 100% sure on my continue logic here, but I think it’s correct. The idea will work, though it’s at least cubic in complexity.