Update str.c and README based on AI code review

homework06/str.c

@@ -5,6 +5,7 @@
 #include <ctype.h>
 #include <stdbool.h>
 #include <stdlib.h>
+#include <string.h>
 
 /* Functions */
 
@@ -59,44 +60,34 @@ void str_title(const char *s, char *w) {
     *w = '\0';
 }
 
-/**
- * Strip characters from back of string (if present).
- * @param   s	    String to strip
- * @param   chars   Characters to strip (if NULL, then all whitespace)
- * @param   w	    Pointer to buffer that holds result of strip
- **/
 void str_rstrip(const char *s, const char *chars, char *w) {
-    bool strip_chars[256] = {0};
+    // Safety checks
+    if (!s || !w) return;
 
-    // Create the lookup table
-    if (chars == NULL) {
-        // If chars is NULL, strip whitespace
-        strip_chars[' '] = true;
+    bool strip_chars[256] = {0};
+    const unsigned char *p = (const unsigned char *)s;
+    size_t length = 0;
+
+    // Build lookup table
+    if (!chars) {
+        // Strip standard whitespace
+        strip_chars[' ']  = true;
         strip_chars['\t'] = true;
         strip_chars['\n'] = true;
     } else {
-        // Otherwise, strip specified characters
-        while (*chars) {
+        for (; *chars; chars++)
             strip_chars[(unsigned char)*chars] = true;
-            chars++;
-        }
     }
 
-    // Copy s to w
-    const char *src = s;
-    char *dst = w;
-    while (*src) {
-        *dst++ = *src++;
-    }
-    *dst = '\0';
+    // Find string length and last non-stripped character
+    while (*p) p++;
+    while (p > (const unsigned char *)s && strip_chars[*(p-1)])
+        p--;
 
-    if (dst > w) {
-        dst--;
-        while (dst >= w && strip_chars[(unsigned char)*dst]) {
-            dst--;
-        }
-        *(dst + 1) = '\0';
-    }
+    // Calculate length and copy
+    length = p - (const unsigned char *)s;
+    memcpy(w, s, length);
+    w[length] = '\0';
 }
 
 /**