binary search in c

c-cpp/15_bsearch/binary_search.c

@@ -0,0 +1,96 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+
+typedef int(*bs)(int *arr, int size, int val); 
+
+int binary_search_r(int *arr, int size, int val)
+{
+	int mid = size / 2;
+	int idx;
+
+	if (arr[mid] == val)
+		return mid;
+
+	// mid == 0 means size == 1
+	// so the only element in array doesn't equal to val
+	if (!mid)
+		return -1;
+
+	if (arr[mid] < val) {
+		idx = binary_search_r(arr + mid + 1, size - mid - 1, val);
+		if (idx != -1)
+			idx += mid + 1;
+	} else {
+		idx = binary_search_r(arr, mid, val);
+	}
+
+	return idx;
+}
+
+int binary_search_i(int *arr, int size, int val)
+{
+	int low = 0, high = size - 1, mid;
+
+	while (low <= high) {
+		mid = (low + high) / 2;
+		if (arr[mid] == val)
+			return mid;
+
+		if (arr[mid] < val)
+			low = mid + 1;
+		else
+			high = mid - 1;
+	}
+
+	return -1;
+}
+
+void iteratioin_test(bs binary_search)
+{
+	int arr[10] = {1, 4, 5, 9, 12, 19, 21, 28, 31, 36};
+	int idx;
+
+	idx = binary_search(arr, 10, 12);
+	if (idx != -1)
+		printf("find 12 at %d\n", idx);
+	else
+		printf("12 not in arr \n");
+
+	idx = binary_search(arr, 10, 13);
+	if (idx != -1)
+		printf("find 13 at %d\n", idx);
+	else
+		printf("13 not in arr \n");
+
+	idx = binary_search(arr, 10, 1);
+	if (idx != -1)
+		printf("find 1 at %d\n", idx);
+	else
+		printf("1 not in arr \n");
+
+	idx = binary_search(arr, 10, 36);
+	if (idx != -1)
+		printf("find 36 at %d\n", idx);
+	else
+		printf("36 not in arr \n");
+
+	idx = binary_search(arr, 10, 31);
+	if (idx != -1)
+		printf("find 31 at %d\n", idx);
+	else
+		printf("31 not in arr \n");
+
+}
+
+int main()
+{
+	printf("=== Test iteration version:\n");
+	iteratioin_test(binary_search_i);
+
+	printf("=== Test recursive version:\n");
+	iteratioin_test(binary_search_r);
+
+	return 0;
+}