merge_sort.html

<script>
  function merge(arr, l, m, r) {
    var n1 = m - l + 1;
    var n2 = r - m;

    // Create temp arrays
    var L = new Array(n1);
    var R = new Array(n2);

    for (var i = 0; i < n1; i++) L[i] = arr[l + i];
    for (var j = 0; j < n2; j++) R[j] = arr[m + 1 + j];

    // Merge the temp arrays back into arr[l..r]

    // Initial index of first subarray
    var i = 0;

    // Initial index of second subarray
    var j = 0;

    // Initial index of merged subarray
    var k = l;

    while (i < n1 && j < n2) {
      if (L[i] <= R[j]) {
        arr[k] = L[i];
        i++;
      } else {
        arr[k] = R[j];
        j++;
      }
      k++;
    }

    // Copy the remaining elements of
    // L[], if there are any
    while (i < n1) {
      arr[k] = L[i];
      i++;
      k++;
    }

    // Copy the remaining elements of
    // R[], if there are any
    while (j < n2) {
      arr[k] = R[j];
      j++;
      k++;
    }
  }

  // l is for left index and r is
  // right index of the sub-array
  // of arr to be sorted */
  function mergeSort(arr, l, r) {
	console.warn(r)
    if (l >= r) {
      return; //returns recursively
    }
    var m = l + parseInt((r - l) / 2);
	// console.warn(m)
    mergeSort(arr, l, m);
    mergeSort(arr, m + 1, r);
    merge(arr, l, m, r);

  }

  var arr = [12, 11, 13, 5, 6, 7];
  var arr_size = arr.length;

  mergeSort(arr, 0, arr_size - 1);
  console.warn(arr)

</script>