counting sort in c

Author: RichardWeiYang

c-cpp/14_sorts/counting_sort.c

@@ -0,0 +1,66 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+
+void dump(int *arr, int size)
+{
+	int i;
+
+	for (i = 0; i < size; i++)
+		printf("%08d\n", arr[i]);
+}
+
+// content in arr must be positive integer
+void counting_sort(int *arr, int size)
+{
+	int max, i;
+	int *count, *tmp;
+
+	if (size <= 1)
+		return;
+
+	max = 0;
+	// find the biggest integer
+	for (i = 0; i < size; i++) {
+		if (max < arr[i])
+			max = arr[i];
+	}
+
+	// init count to 0
+	count = (int*)malloc((max+1) * sizeof(int));
+	tmp = (int*)malloc(size * sizeof(int));
+	if (!count || !tmp)
+		return;
+	memset(count, 0, (max + 1) * sizeof(int));
+
+	// counting
+	for (i = 0; i < size; i++)
+		count[arr[i]]++;
+	for (i = 1; i < max + 1; i++)
+		count[i] = count[i-1] + count[i];
+
+	// iterate arr and put it to the correct index in tmp
+	for (i = 0; i < size; i++){
+		int index = count[arr[i]] - 1;
+		tmp[index] = arr[i];
+		count[arr[i]]--;
+	}
+
+	// move back to arr
+	memcpy(arr, tmp, size * sizeof(int));
+}
+
+void counting_sort_test()
+{
+	int test_data[10] = {3, 23, 98, 1, 27, 36, 52, 89, 76, 44};
+
+	counting_sort(test_data, 10);
+	dump(test_data, 10);
+}
+
+int main()
+{
+	counting_sort_test();
+	return 0;
+}