c: 0392-is-subsequence: use pointers instead of recursion

Recursion is hard to debug and can be difficult to follow.
Using char pointers on the strings is faster, better to debug with, and
easier to understand.

c/0392-is-subsequence.c

@@ -1,18 +1,44 @@
-/*
-Given two strings s and t, return true if s is a subsequence of t, or false otherwise.
+/**
+ * Given two strings s and t, return true if s is a subsequence of t, or false
+ * otherwise. A subsequence of a string is a new string that is formed from the
+ * original string by deleting some (can be none) of the characters without
+ * disturbing the relative positions of the remaining characters. (i.e., "ace"
+ * is a subsequence of "abcde" while "aec" is not).
+ *
+ * Example 1:
 
-Space: O(1)
-Time: O(n)
-*/
+ * Input: s = "abc", t = "ahbgdc"
+ * Output: true
+ *
+ * Example 2:
+ *
+ * Input: s = "axc", t = "ahbgdc"
+ * Output: false
+ *
+ * Constraints:
+ *
+ * 0 <= s.length <= 100
+ * 0 <= t.length <= 104
+ * s and t consist only of lowercase English letters.
+ *
+ * Space: O(1)
+ * Time: O(n)
+ */
 
 bool isSubsequence(char * s, char * t){
-    if (s[0]=='\0'){
-        return true;
-    } else if (t[0]=='\0') {
-        return false;
-    } else if (t[0]==s[0]) {
-        return isSubsequence(s+1, t+1);
-    } else {
-        return isSubsequence(s, t+1);
+    char *s_char = s;
+    char *t_char = t;
+
+    while (*s_char != 0) {
+        if (*t_char == 0) {
+            return false;
+        }
+        else if (*s_char == *t_char) {
+            ++s_char;
+        }
+
+        ++t_char;
     }
+
+    return true;
 }