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| 1 | +/* |
| 2 | +* Merge sort |
| 3 | +*/ |
| 4 | +class Solution { |
| 5 | + fun sortArray(nums: IntArray): IntArray { |
| 6 | + mergeSort(nums, 0, nums.lastIndex) |
| 7 | + return nums |
| 8 | + } |
| 9 | + |
| 10 | + private fun mergeSort(nums: IntArray, left: Int, right: Int) { |
| 11 | + if(left == right) return |
| 12 | + |
| 13 | + val mid = (left + right) / 2 |
| 14 | + mergeSort(nums, left, mid) |
| 15 | + mergeSort(nums, mid + 1, right) |
| 16 | + merge(nums, left, mid, right) |
| 17 | + |
| 18 | + return |
| 19 | + } |
| 20 | + |
| 21 | + private fun merge(nums: IntArray, left: Int, mid: Int, right: Int) { |
| 22 | + val leftPart = nums.copyOfRange(left, mid + 1) |
| 23 | + val rightPart = nums.copyOfRange(mid + 1, right + 1) |
| 24 | + var i = left |
| 25 | + var j = 0 |
| 26 | + var k = 0 |
| 27 | + |
| 28 | + while(j < leftPart.size && k < rightPart.size) { |
| 29 | + if(leftPart[j] <= rightPart[k]) { |
| 30 | + nums[i] = leftPart[j] |
| 31 | + j++ |
| 32 | + }else{ |
| 33 | + nums[i] = rightPart[k] |
| 34 | + k++ |
| 35 | + } |
| 36 | + i++ |
| 37 | + } |
| 38 | + |
| 39 | + while(j < leftPart.size) { |
| 40 | + nums[i] = leftPart[j] |
| 41 | + j++ |
| 42 | + i++ |
| 43 | + } |
| 44 | + |
| 45 | + while(k < rightPart.size) { |
| 46 | + nums[i] = rightPart[k] |
| 47 | + k++ |
| 48 | + i++ |
| 49 | + } |
| 50 | + } |
| 51 | +} |
| 52 | + |
| 53 | +/* |
| 54 | +* Quick sort |
| 55 | +* This will fail testcase 17/19 (used to pass earlier, before adding new testcases), I still added it here for interest. |
| 56 | +* It fails on test case where we have an array with many elements of which all are 2's. This will have quicksort to run as |
| 57 | +* its worst case, which is O(n^2). But on average this will run O(nlogn) |
| 58 | +*/ |
| 59 | +class Solution { |
| 60 | + fun sortArray(nums: IntArray): IntArray { |
| 61 | + |
| 62 | + quickSort(nums, 0, nums.lastIndex) |
| 63 | + return nums |
| 64 | + } |
| 65 | + |
| 66 | + private fun quickSort(nums: IntArray, low: Int, high: Int) { |
| 67 | + if (low < high) { |
| 68 | + val pivotIndex = partition(nums, low, high) |
| 69 | + quickSort(nums, low, pivotIndex - 1) |
| 70 | + quickSort(nums, pivotIndex + 1, high) |
| 71 | + } |
| 72 | + } |
| 73 | + |
| 74 | + private fun partition(nums: IntArray, low: Int, high: Int): Int { |
| 75 | + val pivot = nums[high] |
| 76 | + var i = low |
| 77 | + |
| 78 | + for(j in low until high) { |
| 79 | + if (nums[j] <= pivot) { |
| 80 | + nums.swap(i, j) |
| 81 | + i++ |
| 82 | + } |
| 83 | + } |
| 84 | + |
| 85 | + nums.swap(i, high) |
| 86 | + return i |
| 87 | + } |
| 88 | + |
| 89 | + fun IntArray.swap(i: Int, j: Int) { |
| 90 | + this[i] = this[j].also{ this[j] = this[i] } |
| 91 | + } |
| 92 | +} |
| 93 | + |
| 94 | +/* |
| 95 | +* Heap sort |
| 96 | +*/ |
| 97 | +class Solution { |
| 98 | + fun sortArray(nums: IntArray): IntArray { |
| 99 | + |
| 100 | + heapSort(nums) |
| 101 | + return nums |
| 102 | + } |
| 103 | + |
| 104 | + private fun heapSort(nums: IntArray) { |
| 105 | + val n = nums.size |
| 106 | + |
| 107 | + for(i in (n/2 - 1) downTo 0) |
| 108 | + heapify(nums, n, i) |
| 109 | + |
| 110 | + for(i in n-1 downTo 0) { |
| 111 | + nums.swap(0, i) |
| 112 | + heapify(nums, i, 0) |
| 113 | + } |
| 114 | + } |
| 115 | + |
| 116 | + private fun heapify(nums: IntArray, n: Int, i: Int) { |
| 117 | + var largest = i |
| 118 | + |
| 119 | + val left = 2 * i + 1 |
| 120 | + val right = 2 * i + 2 |
| 121 | + |
| 122 | + if(left < n && nums[left] > nums[largest]) |
| 123 | + largest = left |
| 124 | + if(right < n && nums[right] > nums[largest]) |
| 125 | + largest = right |
| 126 | + |
| 127 | + if(largest != i) { |
| 128 | + nums.swap(i, largest) |
| 129 | + heapify(nums, n, largest) |
| 130 | + } |
| 131 | + } |
| 132 | + |
| 133 | + fun IntArray.swap(i: Int, j: Int) { |
| 134 | + this[i] = this[j].also{ this[j] = this[i] } |
| 135 | + } |
| 136 | +} |
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