Naive solution to subset sum problem in javascript. Given an array of numbers find any combination that adds up to the max.

ArrayAddition

function ArrayAddition(arr) { 

  // first get the max and remove it from the array
  arr.sort(function(a,b) {return b-a;});
  var max = arr[0];
  var arr = arr.slice(1);

 // get all subsets, and filter out subsets whose sum doesn't add up to max.
  var res = subsets(arr, 2).filter(function(sub) {
    return sum(sub) == max;
  });
  // if we now have anything in the resulting array then there is some combination that adds to max.
  return res.length > 0;
}

// sum all numbers in an array
function sum(arr) {
  return arr.reduce(function(p,c) {
    return p+c;
  }, 0);
}

// I stole this bit of magic from stack overflow.
// Quite clever.
var subsets = function(input, size){
  var results = [], result, mask, total = Math.pow(2, input.length);
  for(mask = 0; mask < total; mask++){
    result = [];
    var i = input.length - 1; 
    do{
      if( (mask & (1 << i)) !== 0){
        result.push(input[i]);
      }
    }while(i--);
    if( result.length >= size){
      results.push(result);
    }
  }
  return results; 
};