diff --git a/136_single_number/Makefile b/136_single_number/Makefile
new file mode 100644
index 0000000..f992802
--- /dev/null
+++ b/136_single_number/Makefile
@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test single_number.c
diff --git a/136_single_number/single_number.c b/136_single_number/single_number.c
new file mode 100644
index 0000000..d277c56
--- /dev/null
+++ b/136_single_number/single_number.c
@@ -0,0 +1,22 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+static int singleNumber(int *nums, int numsSize)
+{
+    int i, s = 0;
+    for (i = 0; i < numsSize; i++) {
+        s ^= nums[i];
+    }
+    return s;
+}
+
+int main(int argc, char **argv)
+{
+    int i, count = argc - 1;
+    int *nums = malloc(count * sizeof(int));
+    for (i = 0; i < count; i++) {
+        nums[i] = atoi(argv[i + 1]);
+    }
+    printf("%d\n", singleNumber(nums, count));
+    return 0;
+}
diff --git a/137_single_number_ii/Makefile b/137_single_number_ii/Makefile
new file mode 100644
index 0000000..f992802
--- /dev/null
+++ b/137_single_number_ii/Makefile
@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test single_number.c
diff --git a/137_single_number_ii/single_number.c b/137_single_number_ii/single_number.c
new file mode 100644
index 0000000..bf5beae
--- /dev/null
+++ b/137_single_number_ii/single_number.c
@@ -0,0 +1,71 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#if 0
+static void singleNumber(int *nums, int numsSize)
+{
+    int i, xor = 0;
+    for (i = 0; i < numsSize; i++) {
+        xor ^= nums[i];
+    }
+
+    int mask = 1;
+    while (!(mask & xor)) {
+        mask <<= 1;
+    }
+
+    int zero = 0;
+    int one = 0;
+    for (i = 0; i < numsSize; i++) {
+        if (nums[i] & mask) {
+            one ^= nums[i];
+        } else {
+            zero ^= nums[i];
+        }
+    }
+
+    printf("%d %d\n", zero, one);
+}
+#endif
+
+static int singleNumber(int *nums, int numsSize)
+{
+#if 1
+    int i, j, count[32], mask = 0;
+    for (i = 0; i < 32; i++) {
+        count[i] = 0;
+        for (j = 0; j < numsSize; j++) {
+            if ((1 << i) & nums[j]) {
+                count[i]++;
+            }
+        }
+        mask |= (count[i] % 3) << i;
+    }
+    return mask;
+#else
+    int i, ones = 0, twos = 0, threes = 0;
+    for (i = 0; i < numsSize; i++) {
+        /* `ones & nums[i]` the result is the bitmask which the bits appeared twice */
+        twos |= ones & nums[i]; 
+        /* reset mask twice in `ones` */
+        ones ^= nums[i];
+        /* count the `three` */
+        threes = ones & twos;
+        /* clear the `ones` and `twos` if the i-th bit had appeared three times. */
+        ones &= ~threes;
+        twos &= ~threes;
+    }
+    return ones;
+#endif
+}
+
+int main(int argc, char **argv)
+{
+    int i, count = argc - 1;
+    int *nums = malloc(count * sizeof(int));
+    for (i = 0; i < count; i++) {
+        nums[i] = atoi(argv[i + 1]);
+    }
+    printf("%d\n", singleNumber(nums, count));
+    return 0;
+}