quick sort (#90)

Author: realDuYuanChao

sorts/quick_sort.c

@@ -2,17 +2,26 @@
 #include <stdlib.h>
 #include <time.h>
 
+void swap(int *arr, int i, int j) {
+    int temp = arr[i];
+    arr[i] = arr[j];
+    arr[j] = temp;
+}
+
 int partition(int *arr, int low, int high) {
     int pivot = arr[low];
     while (low < high) {
         while (low < high && arr[high] >= pivot) {
             high--;
         }
-        arr[low] = arr[high];
         while (low < high && arr[low] <= pivot) {
             low++;
         }
-        arr[high] = arr[low];
+        if (low < high) {
+            swap(arr, low, high);
+            low++;
+            high--;
+        }
     }
     arr[low] = pivot;
     return low;

sorts/quick_sort_easy_partition.c

@@ -0,0 +1,56 @@
+#include <assert.h>
+#include <stdlib.h>
+#include <time.h>
+
+int partition(int *arr, int low, int high) {
+    int len = high - low + 1;
+    int temp[len];
+    int j = 0;
+    int k = len - 1;
+    int pivot = arr[low];
+    for (int i = low + 1; i <= high; ++i) {
+        if (arr[i] <= pivot) {
+            temp[j] = arr[i];
+            j++;
+        } else {
+            temp[k] = arr[i];
+            k--;
+        }
+    }
+    assert(j == k);
+    temp[j] = pivot;
+    for (int i = 0; i < len; ++i) {
+        arr[low + i] = temp[i];
+    }
+    return low + j; /* return low + k */
+}
+
+void quickSort(int *arr, int low, int high) {
+    if (low < high) {
+        int pivotIndex = partition(arr, low, high);
+        quickSort(arr, low, pivotIndex - 1);
+        quickSort(arr, pivotIndex + 1, high);
+    }
+}
+
+void test() {
+    const int size = 10;
+    int *arr = (int *) calloc(size, sizeof(int));
+
+    /* generate size random numbers from 0 to 100 */
+    for (int i = 0; i < size; i++) {
+        arr[i] = rand() % 100;
+    }
+    quickSort(arr, 0, size - 1);
+    for (int i = 0; i < size - 1; ++i) {
+        assert(arr[i] <= arr[i + 1]);
+    }
+    free(arr);
+}
+
+int main() {
+    /* initial random number generator */
+    srand(time(NULL));
+    test();
+    return 0;
+}