fix two answers to make them correct (100 pts.)

semester1/pset12/1-3-GetVowel.c

@@ -1,5 +1,4 @@
 // https://bbc3502.hopto.org/c2021/index.php/home-17/590-3
-/* ⚠*** This code is not perfect *** */
 #include <stdio.h>
 
 //将只包含小写字母的字符串str中的元音字母复制到字符数组vowel,并返回元音字符的个数。
@@ -23,14 +22,17 @@ int main() {
 #include <string.h>
 #pragma GCC optimize("Ofast,inline")
 int getVowel(char str[], char vowel[]) {
-  char vowelstr[] = {'a', 'e', 'i', 'o', 'u', '\0'};
+  char vowelstr[] = {'a', 'e', 'i', 'o', 'u'};
   int len = 0;
   for (int i = 0, n = strlen(str); i < n; i++) {
-    for (int j = 0, m = strlen(vowelstr); j < m; j++) {
+    for (int j = 0, m = sizeof(vowelstr) / sizeof(char); j < m; j++) {
       if (vowelstr[j] == str[i]) {
         vowel[len++] = str[i];
       }
     }
   }
+  // vowel[len] is a trash value, and will lead to undefined behavior in some
+  // cases
+  vowel[len] = '\0';
   return len;
 }

semester1/pset12/2-1-paren.c

@@ -11,9 +11,14 @@ int main(void) {
 
   // Process string
   int count = 0;
-  for (int i = 0, n = strlen(str); i < n; i++) {
+  int mismatch = 0;
+  for (int i = 0, n = strlen(str); i < n && !mismatch; i++) {
     if (str[i] == '(') {
-      count++;
+      if (count < 0) { // )(
+        mismatch = 1;
+      } else {
+        count++;
+      }
     } else if (str[i] == ')') {
       count--;
     }