diff --git a/semester1/pset12/1-3-INCORRECT-GetVowel.c b/semester1/pset12/1-3-INCORRECT-GetVowel.c
index d562652..7670d77 100644
--- a/semester1/pset12/1-3-INCORRECT-GetVowel.c
+++ b/semester1/pset12/1-3-INCORRECT-GetVowel.c
@@ -1,3 +1,4 @@
+// https://bbc3502.hopto.org/c2021/index.php/home-17/590-3
 /* ⚠*** This code is not perfect *** */
 #include <stdio.h>
 
@@ -22,10 +23,10 @@ int main() {
 #include <string.h>
 #pragma GCC optimize("Ofast,inline")
 int getVowel(char str[], char vowel[]) {
-  char vowelstr[] = {'a', 'e', 'i', 'o', 'u'};
+  char vowelstr[] = {'a', 'e', 'i', 'o', 'u', '\0'};
   int len = 0;
   for (int i = 0, n = strlen(str); i < n; i++) {
-    for (int j = 0; j < 5; j++) {
+    for (int j = 0, m = strlen(vowelstr); j < m; j++) {
       if (vowelstr[j] == str[i]) {
         vowel[len++] = str[i];
       }
diff --git a/semester1/pset12/2-1-paren.c b/semester1/pset12/2-1-paren.c
new file mode 100644
index 0000000..0a86695
--- /dev/null
+++ b/semester1/pset12/2-1-paren.c
@@ -0,0 +1,29 @@
+// https://bbc3502.hopto.org/c2021/index.php/home-17/591-1
+// This code should get 100 points but due to the shitty pintia, it gets 90.
+#include <stdio.h>
+#include <string.h>
+#define MAXLEN 101
+
+int main(void) {
+  char str[MAXLEN];
+  // fgets is not gets
+  fgets(str, MAXLEN, stdin);
+
+  // Process string
+  int count = 0;
+  for (int i = 0, n = strlen(str); i < n; i++) {
+    if (str[i] == '(') {
+      count++;
+    } else if (str[i] == ')') {
+      count--;
+    }
+  }
+
+  // Validate
+  if (count != 0) {
+    printf("parentheses do not match!\n");
+  } else {
+    printf("parentheses match!\n");
+  }
+  return 0;
+}
diff --git a/semester1/pset12/2-2-IDnumber.c b/semester1/pset12/2-2-IDnumber.c
new file mode 100644
index 0000000..c17ee9a
--- /dev/null
+++ b/semester1/pset12/2-2-IDnumber.c
@@ -0,0 +1,43 @@
+#include <stdio.h>
+#include <stdlib.h>
+#pragma GCC optimize("Ofast,inline")
+#define MAXLEN 18
+
+// returns 1 if valid, otherwise 0
+int validate(char *id);
+
+int main(void) {
+  char *id = malloc(sizeof(char) * MAXLEN);
+  int lines;
+
+  scanf("%d", &lines);
+
+  for (int i = 0; i < lines; i++) {
+		scanf("%s", id);
+    if (validate(id)) {
+      printf("right\n");
+    } else {
+      printf("wrong\n");
+    }
+  }
+
+  free(id);
+  return 0;
+}
+
+int validate(char *id) {
+  char lasttable[] = "10X98765432";
+  int factor[] = {7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2};
+  int last = 0;
+
+  for (int i = 0; i < 17; i++) {
+    last += (id[i] - '0') * factor[i];
+  }
+
+  last = last % 11;
+  if (lasttable[last] == id[17]) {
+    return 1;
+  } else {
+    return 0;
+  }
+}
diff --git a/semester1/pset12/2-3-analyze.c b/semester1/pset12/2-3-analyze.c
new file mode 100644
index 0000000..a78a2ac
--- /dev/null
+++ b/semester1/pset12/2-3-analyze.c
@@ -0,0 +1,33 @@
+#include <stdio.h>
+#include <string.h>
+#pragma GCC optimize("Ofast,inline")
+#define MAXLEN 100
+
+int main(void) {
+  char string[MAXLEN];
+  scanf("%s", string);
+
+  char hashA[26] = {};
+  char hasha[26] = {};
+
+	// Store values to hash table
+  for (int i = 0, j = strlen(string); i < j; i++) {
+    if (string[i] >= 'A' && string[i] <= 'Z') {
+      hashA[string[i] - 'A']++;
+    } else if (string[i] >= 'a' && string[i] <= 'z') {
+      hasha[string[i] - 'a']++;
+    }
+  }
+
+	for (int i = 0; i < 26; i++) {
+		if (hashA[i]) {
+			printf("The character %c has presented %i times.\n", i + 'A', hashA[i]);
+		}
+	}
+	for (int i = 0; i < 26; i++) {
+		if (hasha[i]) {
+			printf("The character %c has presented %i times.\n", i + 'a', hasha[i]);
+		}
+	}
+  return 0;
+}
diff --git a/semester1/pset12/2-4-OrderedPrint.c b/semester1/pset12/2-4-OrderedPrint.c
new file mode 100644
index 0000000..c0c23b6
--- /dev/null
+++ b/semester1/pset12/2-4-OrderedPrint.c
@@ -0,0 +1,31 @@
+#include <stdio.h>
+#include <stdlib.h>
+#pragma GCC optimize("Ofast,inline")
+#define MAXLEN 31
+
+int main(void) {
+  int lines;
+  scanf("%d", &lines);
+
+  // Fancy way of allocating memory to 2d array
+  char *arr[lines];
+  for (int i = 0; i < lines; i++) {
+    arr[i] = malloc(sizeof(char) * MAXLEN);
+  }
+
+  // Populate the 2d array
+  for (int i = 0; i < lines; i++) {
+    scanf("%s", arr[i]);
+  }
+
+  // Populate the order array
+  int order[lines];
+  for (int i = 0; i < lines; i++) {
+    scanf("%d", &order[i]);
+  }
+
+  for (int i = 0; i < lines; i++) {
+    printf("%s\n", arr[order[i]]);
+  }
+  return 0;
+}