Coding Puzzles: Thinking in code - 2sum

jsbin.nekog.js

var createMapping = function(numbers) {
  
  var mapping = {},
      size = numbers.length;
  
  for (var i = 0; i < size; i++) {
      mapping[numbers[i]] = i;
  }
  
  return mapping;
};

var getPairs = function(numbers, target, mapping){

  var size = numbers.length,
      result = [];
  
  for (var i = 0; i < size; i++) {
    
    var searched = target - numbers[i];
    if (typeof mapping[searched] !== 'undefined') {
      result.push(i+1);
      result.push(mapping[searched]+1);
      break;
    }
  }
  
  return result;
  
};

var arr = [2, 7, 11, 15];
//target 9

var mapping = createMapping(arr);

console.log(mapping);

console.log(getPairs(arr, 9, mapping));