Searches for a triplet of values in an array that sum to the target value. Returns null if such a triplet doesn't exist.

faster_triple.js

function findClosest(items, value){
  // a modified binary search that returns the last
  // index checked, whether or not it had the correct value
  var startIndex = 0;
  var stopIndex = items.length - 1;
  var middle = Math.floor((stopIndex + startIndex)/2);

  while(items[middle] != value && startIndex < stopIndex){
    middle = Math.floor((stopIndex + startIndex)/2);
    if (value < items[middle]){
      stopIndex = middle - 1;
    } else if (value > items[middle]){
      startIndex = middle + 1;
    }
  }

  return middle;
}

function fasterThreeTuple( array, target ) {
  if (isNaN(target)){return null;}
  array.sort();
  var j = 0;
  var k = array.length - 1;
  var i = 0;
  while(k > j) {
    i = findClosest(array, array[k]-array[j]);
    summation = array[i] + array[j] + array[k];
    if (summation === target) {return [i,j,k];}
    if (summation > target) {k--;}
    if (summation < target) {j++;}
  }
  return null;
}

// tests
var set = [0,1,2,3,-4,5];
var testTargets = [2, 4, 100, "100 million"];
print(set.sort());
for (var i = 0; i < testTargets.length; i++){
  var result = crazyFast(set, testTargets[i]);
  print((result === null) ? "No dice." : [set[result[0]],set[result[1]],set[result[2]]]);
}