Allow for palindromes with non-alpha characters

c/palindrome.c

@@ -1,8 +1,18 @@
-int palindrome(const char *str, unsigned len) {
-  unsigned idx = 0;
+#include <ctype.h>
 
-  for(; idx < (len - (len % 2)) / 2; idx += 1) {
-    if(str[idx] != str[len - idx - 1]) {
+int palindrome(const char *str, unsigned len) {
+  const char *start = str;
+  const char *end = str + len - 1;
+
+  while(start < end) {
+    if(!isalpha(*start)) {
+      start += 1;
+    } else if(!isalpha(*end)) {
+      end -= 1;
+    } else if(tolower(*start) == tolower(*end)) {
+      start += 1;
+      end -= 1;
+    } else {
       return 0;
     }
   }