September 2017 Update

Task/Sorting-algorithms-Quicksort/C/sorting-algorithms-quicksort-1.c

@@ -0,0 +1,44 @@
+#include <stdio.h>
+
+void quicksort(int *A, int len);
+
+int main (void) {
+  int a[] = {4, 65, 2, -31, 0, 99, 2, 83, 782, 1};
+  int n = sizeof a / sizeof a[0];
+
+  int i;
+  for (i = 0; i < n; i++) {
+    printf("%d ", a[i]);
+  }
+  printf("\n");
+
+  quicksort(a, n);
+
+  for (i = 0; i < n; i++) {
+    printf("%d ", a[i]);
+  }
+  printf("\n");
+
+  return 0;
+}
+
+void quicksort(int *A, int len) {
+  if (len < 2) return;
+
+  int pivot = A[len / 2];
+
+  int i, j;
+  for (i = 0, j = len - 1; ; i++, j--) {
+    while (A[i] < pivot) i++;
+    while (A[j] > pivot) j--;
+
+    if (i >= j) break;
+
+    int temp = A[i];
+    A[i]     = A[j];
+    A[j]     = temp;
+  }
+
+  quicksort(A, i);
+  quicksort(A + i, len - i);
+}

Task/Sorting-algorithms-Quicksort/C/sorting-algorithms-quicksort-2.c

@@ -0,0 +1,29 @@
+#include <stdlib.h>     // REQ: rand()
+
+void swap(int *a, int *b) {
+  int c = *a;
+  *a = *b;
+  *b = c;
+}
+
+int partition(int A[], int p, int q) {
+  swap(&A[p + (rand() % (q - p + 1))], &A[q]);   // PIVOT = A[q]
+
+  int i = p - 1;
+  for(int j = p; j <= q; j++) {
+    if(A[j] <= A[q]) {
+      swap(&A[++i], &A[j]);
+    }
+  }
+
+  return i;
+}
+
+void quicksort(int A[], int p, int q) {
+  if(p < q) {
+    int pivotIndx = partition(A, p, q);
+
+    quicksort(A, p, pivotIndx - 1);
+    quicksort(A, pivotIndx + 1, q);
+  }
+}

Task/Sorting-algorithms-Quicksort/C/sorting-algorithms-quicksort.c

@@ -1,33 +0,0 @@
-#include <stdio.h>
-
-void quick_sort (int *a, int n) {
-    int i, j, p, t;
-    if (n < 2)
-        return;
-    p = a[n / 2];
-    for (i = 0, j = n - 1;; i++, j--) {
-        while (a[i] < p)
-            i++;
-        while (p < a[j])
-            j--;
-        if (i >= j)
-            break;
-        t = a[i];
-        a[i] = a[j];
-        a[j] = t;
-    }
-    quick_sort(a, i);
-    quick_sort(a + i, n - i);
-}
-
-int main (void) {
-    int a[] = {4, 65, 2, -31, 0, 99, 2, 83, 782, 1};
-    int n = sizeof a / sizeof a[0];
-    int i;
-    for (i = 0; i < n; i++)
-        printf("%d%s", a[i], i == n - 1 ? "\n" : " ");
-    quick_sort(a, n);
-    for (i = 0; i < n; i++)
-        printf("%d%s", a[i], i == n - 1 ? "\n" : " ");
-    return 0;
-}