diff --git a/semester1/pset11/2-2storage.c b/semester1/pset11/2-2-storage.c
similarity index 100%
rename from semester1/pset11/2-2storage.c
rename to semester1/pset11/2-2-storage.c
diff --git a/semester1/pset12/1-1-ReverseChar.c b/semester1/pset12/1-1-ReverseChar.c
new file mode 100644
index 0000000..053e6fc
--- /dev/null
+++ b/semester1/pset12/1-1-ReverseChar.c
@@ -0,0 +1,38 @@
+#include <stdio.h>
+#pragma GCC optimize("Ofast,inline")
+
+//将字符串str中的内容反向打印的函数
+void reversePrint(char str[]);
+
+int main() {
+  char s[100];
+
+  scanf("%s", s);
+  reversePrint(s);
+  printf("\n");
+
+  return 0;
+}
+
+/* 请在这里填写答案 */
+#include <stdlib.h>
+#include <string.h>
+void reversePrint(char str[]) {
+  if (str == NULL) {
+    return;
+  }
+  if (strlen(str) == 1) {
+    printf("%c", str[0]);
+  } else {
+    char *tmp = malloc(sizeof(char) * strlen(str));
+    /* Why this:
+     * char *tmp = malloc(sizeof(char) * (strlen(str) - 1));
+     * doesn't work? */
+    for (int i = 1, n = strlen(str), j = 0; i < n; i++, j++) {
+      tmp[j] = str[i];
+    }
+    reversePrint(tmp);
+    free(tmp);
+    printf("%c", str[0]);
+  }
+}
diff --git a/semester1/pset12/1-2-count.c b/semester1/pset12/1-2-count.c
new file mode 100644
index 0000000..87122cb
--- /dev/null
+++ b/semester1/pset12/1-2-count.c
@@ -0,0 +1,47 @@
+#include <stdio.h>
+
+#define MAXLEN 110
+
+int isPrime(int n); //判断一个整数是否是质数，是则返回1，否则返回0
+int getResult(char word[]);
+
+int main() {
+  char word[MAXLEN];
+
+  scanf("%s", word);
+  printf("%d\n", getResult(word));
+
+  return 0;
+}
+
+/* 请在这里填写答案 */
+int getResult(char word[]) {
+  int hashtable[26] = {};
+
+  // Load word into hash table
+  for (int i = 0; word[i] != '\0'; i++) {
+    hashtable[word[i] - 'a']++;
+  }
+
+  // Analyze words
+  int max = 0;
+  int min = MAXLEN;
+  for (int i = 0; i < 26; i++) {
+		// If hashtable[i] == 0, the letter is not in the word.
+    if (hashtable[i] == 0) {
+      continue;
+    }
+    if (hashtable[i] > max) {
+      max = hashtable[i];
+    }
+    if (hashtable[i] < min) {
+      min = hashtable[i];
+    }
+  }
+
+  if (isPrime(max - min)) {
+    return max - min;
+  } else {
+    return -1;
+  }
+}
diff --git a/semester1/pset12/1-3-INCORRECT-GetVowel.c b/semester1/pset12/1-3-INCORRECT-GetVowel.c
new file mode 100644
index 0000000..d562652
--- /dev/null
+++ b/semester1/pset12/1-3-INCORRECT-GetVowel.c
@@ -0,0 +1,35 @@
+/* ⚠*** 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。
+int getVowel(char str[], char vowel[]);
+
+int main() {
+  char vowel[101], str[101]; //每个数组都至少要101个字节
+  int len;
+
+  scanf("%s", str);           //读入字符串
+  len = getVowel(str, vowel); //复制
+  if (len > 0)
+    printf("%d %s\n", len, vowel); //输出复制后结果
+  else
+    printf("%d\n", len); //仅输出长度
+
+  return 0;
+}
+
+/* 请在这里填写答案 */
+#include <string.h>
+#pragma GCC optimize("Ofast,inline")
+int getVowel(char str[], char vowel[]) {
+  char vowelstr[] = {'a', 'e', 'i', 'o', 'u'};
+  int len = 0;
+  for (int i = 0, n = strlen(str); i < n; i++) {
+    for (int j = 0; j < 5; j++) {
+      if (vowelstr[j] == str[i]) {
+        vowel[len++] = str[i];
+      }
+    }
+  }
+  return len;
+}