diff --git a/0003_longest_substring_without_repeat/longest_substring_without_repeat.c b/0003_longest_substring_without_repeat/longest_substring_without_repeat.c
index 7af62c6..51c7c27 100644
--- a/0003_longest_substring_without_repeat/longest_substring_without_repeat.c
+++ b/0003_longest_substring_without_repeat/longest_substring_without_repeat.c
@@ -5,31 +5,19 @@
 
 int lengthOfLongestSubstring(char *s)
 {
-    int offset[128];
-    int max_len = 0;
+    int count[256] = {0};
     int len = 0;
-    int index = 0;
+    int i, j;
 
-    memset(offset, 0xff, sizeof(offset));
-    while (*s != '\0') {
-        if (offset[*s] == -1) {
-            len++;
-        } else {
-            if (index - offset[*s] > len) {
-                /* not included in sliding window, go on increasing */
-                len++;
-            } else {
-                /* repetition in sliding window, count from scratch */
-	        len = index - offset[*s];
-            }
+    for (i = 0, j = 0; s[i] != '\0'; i++) {
+        count[s[i]]++;
+        while (count[s[i]] > 1) {
+            len = i - j > len ? i - j : len;
+            count[s[j++]] -= 1;
         }
-        if (len > max_len) {
-            max_len = len;
-        }
-        offset[*s++] = index++;
     }
 
-    return max_len;
+    return i - j > len ? i - j : len;
 }
 
 int main(int argc, char **argv)
diff --git a/0003_longest_substring_without_repeat/longest_substring_without_repeat.cc b/0003_longest_substring_without_repeat/longest_substring_without_repeat.cc
index 08a12e2..af643ca 100644
--- a/0003_longest_substring_without_repeat/longest_substring_without_repeat.cc
+++ b/0003_longest_substring_without_repeat/longest_substring_without_repeat.cc
@@ -5,26 +5,18 @@ using namespace std;
 class Solution {
 public:
     int lengthOfLongestSubstring(string s) {
-        vector<int> indexes(128, -1);
-        int max_len = 0;
+        vector<int> count(256);
         int len = 0;
+        int i, j;
 
-        for (int i = 0; i < s.length(); i++) {
-            if (indexes[s[i]] == -1) {
-                len++;
-            } else {
-                if (i - indexes[s[i]] > len) {
-                    /* not included in sliding window, go on increasing */
-                    len++;
-                } else {
-                    /* repetition in sliding window, count from scratch */
-                    len = i - indexes[s[i]];
-                }
+        for (i = 0, j = 0; i < s.length(); i++) {
+            count[s[i]]++;
+            while (count[s[i]] > 1) {
+                len = i - j > len ? i - j : len;
+                count[s[j++]] -= 1;
             }
-            max_len = max(max_len, len);
-            indexes[s[i]] = i;
         }
 
-        return max_len;
+        return i - j > len ? i - j : len;
     }
 };
diff --git a/0076_minimum_window_substring/window_substring.c b/0076_minimum_window_substring/window_substring.c
index a9e87ab..41f5d0b 100644
--- a/0076_minimum_window_substring/window_substring.c
+++ b/0076_minimum_window_substring/window_substring.c
@@ -2,6 +2,17 @@
 #include <stdlib.h>
 #include <string.h>
 
+
+/* sliding window pattern 
+ * while (r < size) {
+ *     // check target condition
+ *     while (target_condition) {
+ *         // calculate minimum length
+ *         // iterate left indicator
+ *     }
+ *     // iterate right indicator
+ * }
+ */
 static char *minWindow(char *s, char *t)
 {
     int i, j, count[256] = { 0 };
@@ -42,8 +53,7 @@ static char *minWindow(char *s, char *t)
         memcpy(result, s + start, min_len);
         result[min_len] = '\0';
     } else {
-        result = malloc(1);
-        result[0] = '\0';
+        result = "";
     }
 
     return result;