See: http://www.glassdoor.com/Interview/You-are-given-a-collection-of-M-arrays-with-N-integers-Every-array-is-sorted-Develop-an-algorithm-to-combine-each-array-i-QTN_1195702.htm

merge-sorted-lists.js

//
// See: http://www.glassdoor.com/Interview/You-are-given-a-collection-of-M-arrays-with-N-integers-Every-array-is-sorted-Develop-an-algorithm-to-combine-each-array-i-QTN_1195702.htm
//
// You are given a collection of M arrays with N integers. Every array is sorted.
// Develop an algorithm to combine each array into one sorted array.
//

var mergeSortedLists = (function () {

  /**
   * Merge (given two sorted arrays, return a single sorted array)
   *
   * @param {array} left
   * @param {array} right
   * @return {array}
   */
  var merge = function (left, right) {

   // store resulting array
   var sorted = [];

   // loop through lists and compare elements front to back, until either list is empty
   while (left.length > 0 && right.length > 0) {
     (left[0] <= right[0]) ? sorted.push(left.shift()) : sorted.push(right.shift());
   }

   // add any remaining items
   while (left.length > 0) sorted.push(left.shift());
   while (right.length > 0) sorted.push(right.shift());

   // return sorted list
   return sorted;

  };

  return function (arrays) {
    return arrays.reduce(function (acc, curr) {
      return merge(acc, curr);
    }, []);
  };

}());