add quick sort

Author: AaronLinRC

src/main/kotlin/sort/QuickSort.kt

@@ -0,0 +1,40 @@
+package sort
+
+import org.junit.Test
+import util.swap
+
+// 随机数下，数学期望 NLogN
+// 无随机数情况，最差情况，单调序列 O(n*n) -> 由于划分值打得很偏
+object QuickSort {
+    fun sort(array: IntArray) {
+        rec(0, array.lastIndex, array)
+    }
+
+    fun rec(l: Int, r: Int, array: IntArray) {
+        if (!(l in array.indices && r in array.indices && l < r)) return
+
+        val arr = partition(l, r, array)
+        rec(l, arr[0], array)
+        rec(arr[1], r, array)
+    }
+
+    fun partition(l: Int, r: Int, array: IntArray): IntArray {
+        val k = array[r]
+        var p1 = l - 1
+        var p2 = l
+        var p3 = r
+        while (p2 < p3) {
+            if (array[p2] < k) {
+                array.swap(p2, ++p1)
+                p2++
+            } else if (array[p2] > k) {
+                array.swap(p2, --p3)
+            } else {
+                p2++
+            }
+        }
+        array.swap(r, p2)
+        println(array.joinToString(","))
+        return intArrayOf(p1, p2)
+    }
+}

src/main/kotlin/sort/TestSort.kt

@@ -5,8 +5,6 @@ import org.junit.Test
 import util.sameAs
 
 class TestSort {
-    private val arr = intArrayOf(2, 45, 3462, 34, 6, 34, 754, 45, 6, 2)
-
     @Test
     fun testSelection() {
         repeat(5) {
@@ -41,13 +39,23 @@ class TestSort {
     }
 
     @Test
-    fun testMerge(){
+    fun testMerge() {
         repeat(5) {
             var array1 = Logarithm.generateRandomArray(50, 50)
             var array2 = array1.clone()
             array1 = MergeSort.sort(array1)
             array2.sort()
-            println("Merge sort:${array1.joinToString(",")}")
+            Assert.assertTrue(array2.sameAs(array1))
+        }
+    }
+
+    @Test
+    fun testQuick() {
+        repeat(5) {
+            val array1 = Logarithm.generateRandomArray(50, 50)
+            val array2 = array1.clone()
+            array2.sort()
+            QuickSort.sort(array1)
             Assert.assertTrue(array2.sameAs(array1))
         }
     }

src/main/kotlin/util/Array.kt

@@ -1,12 +1,12 @@
 package util
 
 fun IntArray.swap(i: Int, j: Int) {
-    this[i] = this[i] xor this[j]
-    this[j] = this[i] xor this[j]
-    this[i] = this[i] xor this[j]
-//    val temp = this[i]
-//    this[i] = this[j]
-//    this[j] = temp
+//    this[i] = this[i] xor this[j]
+//    this[j] = this[i] xor this[j]
+//    this[i] = this[i] xor this[j]
+    val temp = this[i]
+    this[i] = this[j]
+    this[j] = temp
 }
 
 fun IntArray.sameAs(intArray: IntArray): Boolean {