From e43024e8f5cb147afb24865593c43791e09756e9 Mon Sep 17 00:00:00 2001
From: Du Yuanchao <shellhub.me@gmail.com>
Date: Tue, 21 Jul 2020 23:16:11 +0800
Subject: [PATCH] bubble sort optimization (#573)

---
 sorting/bubble_sort.c | 96 ++++++++++++++++++++++++++++---------------
 1 file changed, 62 insertions(+), 34 deletions(-)

diff --git a/sorting/bubble_sort.c b/sorting/bubble_sort.c
index de203329..8bd4edf2 100644
--- a/sorting/bubble_sort.c
+++ b/sorting/bubble_sort.c
@@ -1,20 +1,33 @@
-// sorting of array list using bubble sort
+/**
+ * @file
+ * @brief [Bubble sort](https://en.wikipedia.org/wiki/Bubble_sort) algorithm
+ * implementation
+ */
+#include <assert.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <time.h>
 
-/*Displays the array, passed to this method*/
-void display(int *arr, int n)
+/**
+ * Display elements of array
+ * @param arr array to be display
+ * @param n length of array
+ */
+void display(const int *arr, int n)
 {
-    int i;
-    for (i = 0; i < n; i++)
+    for (int i = 0; i < n; i++)
     {
         printf("%d ", arr[i]);
     }
-
     printf("\n");
 }
 
-/*Swap function to swap two values*/
+/**
+ * Swap two values by using pointer
+ * @param first first pointer of first number
+ * @param second second pointer of second number
+ */
 void swap(int *first, int *second)
 {
     int temp = *first;
@@ -22,46 +35,61 @@ void swap(int *first, int *second)
     *second = temp;
 }
 
-/*This is where the sorting of the array takes place
- arr[] --- Array to be sorted
- size --- Array Size
+/**
+ * Bubble sort algorithm implementation
+ * @param arr array to be sorted
+ * @param size size of array
  */
 void bubbleSort(int *arr, int size)
 {
     for (int i = 0; i < size - 1; i++)
-    {
+    {                         /* for each array index */
+        bool swapped = false; /* flag to check if any changes had to be made */
+        /* perform iterations until no more changes were made or outer loop
+            executed for all array indices */
         for (int j = 0; j < size - 1 - i; j++)
-        {
+        { /* for each element in the array */
             if (arr[j] > arr[j + 1])
-            {
+            { /* if the order of successive elements needs update */
                 swap(&arr[j], &arr[j + 1]);
+                swapped = true; /* set flag */
             }
         }
+        if (!swapped)
+        {
+            /* since no more updates we made, the array is already sorted
+                this is an optimization for early termination */
+            break;
+        }
     }
 }
 
+/**
+ * Test function
+ */
+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;
+    }
+    bubbleSort(arr, size);
+    for (int i = 0; i < size - 1; ++i)
+    {
+        assert(arr[i] <= arr[i + 1]);
+    }
+    free(arr);
+}
+
+/** Driver Code */
 int main(int argc, const char *argv[])
 {
-    int n;
-    printf("Enter size of array:\n");
-    scanf("%d", &n);  // E.g. 8
-
-    printf("Enter the elements of the array\n");
-    int i;
-    int *arr = (int *)malloc(n * sizeof(int));
-    for (i = 0; i < n; i++)
-    {
-        scanf("%d", &arr[i]);
-    }
-
-    printf("Original array: ");
-    display(arr, n);  // Original array : 10 11 9 8 4 7 3 8
-
-    bubbleSort(arr, n);
-
-    printf("Sorted array: ");
-    display(arr, n);  // Sorted array : 3 4 7 8 8 9 10 11
-
-    free(arr);
+    /* Intializes random number generator */
+    srand(time(NULL));
+    test();
     return 0;
 }