From df569175b6345489bfd9671f2cedf85f31298509 Mon Sep 17 00:00:00 2001
From: begeekmyfriend <begeekmyfriend@gmail.com>
Date: Tue, 1 Aug 2017 17:48:50 +0800
Subject: [PATCH] Gray code

Signed-off-by: begeekmyfriend <begeekmyfriend@gmail.com>
---
 089_gray_code/Makefile    |  2 ++
 089_gray_code/gray_code.c | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+)
 create mode 100644 089_gray_code/Makefile
 create mode 100644 089_gray_code/gray_code.c

diff --git a/089_gray_code/Makefile b/089_gray_code/Makefile
new file mode 100644
index 0000000..dbe10ea
--- /dev/null
+++ b/089_gray_code/Makefile
@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test gray_code.c
diff --git a/089_gray_code/gray_code.c b/089_gray_code/gray_code.c
new file mode 100644
index 0000000..6f72ce6
--- /dev/null
+++ b/089_gray_code/gray_code.c
@@ -0,0 +1,38 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+/**
+ ** Return an array of size *returnSize.
+ ** Note: The returned array must be malloced, assume caller calls free().
+ **/
+int* grayCode(int n, int* returnSize) {
+    if (n < 0) {
+        return NULL;
+    }
+
+    int i, count = 1 << n;
+    int *codes = malloc(count * sizeof(int));
+    for (i = 0; i < count; i++) {
+        codes[i] = (i >> 1) ^ i;
+    }
+
+    *returnSize = 1 << n;
+    return codes;
+}
+
+int main(int argc, char **argv)
+{
+    if (argc != 2) {
+        fprintf(stderr, "Usage: ./test n\n");
+        exit(-1);
+    }
+
+    int i, count;
+    int *list = grayCode(atoi(argv[1]), &count);
+    for (i = 0; i < count; i++) {
+        printf("%d ", list[i]);
+    }
+    printf("\n");
+
+    return 0;
+}