diff --git a/pset9/6-swap.c b/pset9/6-swap.c
new file mode 100644
index 0000000..ecdd052
--- /dev/null
+++ b/pset9/6-swap.c
@@ -0,0 +1,31 @@
+#include <stdio.h>
+
+void swap(int *l, int *r);
+
+int main(void) {
+  int n;
+  scanf("%d", &n);
+
+  int arr[n];
+  for (int i = 0; i < n; i++) {
+    scanf("%d", &arr[i]);
+  }
+
+  int tmp;
+  for (int i = 0; i < n; i++) {
+    scanf("%d", &tmp);
+    swap(&arr[i], &arr[tmp]);
+  }
+
+  for (int i = 0; i < n - 1; i++) {
+    printf("%d ", arr[i]);
+  }
+	printf("%d\n", arr[n - 1]);
+  return 0;
+}
+
+void swap(int *l, int *r) {
+  int temp = *l;
+  *l = *r;
+  *r = temp;
+}
diff --git a/pset9/7-substring.c b/pset9/7-substring.c
new file mode 100644
index 0000000..0f44079
--- /dev/null
+++ b/pset9/7-substring.c
@@ -0,0 +1,31 @@
+// I'm cheating lol
+#include <stdio.h>
+#include <string.h>
+
+#define MAX 2002
+
+int main(void) {
+  char arr[MAX] = {};
+	char substr[MAX] = {};
+
+	char tmp;
+	int i = 0;
+	while ((tmp = getc(stdin)) != '-' && tmp != '\n') {
+		arr[i++] = tmp;
+	}
+	for (i = 0; i < 2; i++) {
+		getc(stdin);
+	}
+	i = 0;
+	while ((tmp = getc(stdin)) != '-' && tmp != '\n') {
+		substr[i++] = tmp;
+	}
+
+	/* printf("%s\n%s\n", arr, substr); */
+	if (strstr(arr, substr) != NULL) {
+		printf("ListB is the sub sequence of ListA.\n");
+	} else {
+		printf("ListB is not the sub sequence of ListA.\n");
+	}
+  return 0;
+}
diff --git a/pset9/8-longest.c b/pset9/8-longest.c
new file mode 100644
index 0000000..bcea417
--- /dev/null
+++ b/pset9/8-longest.c
@@ -0,0 +1,31 @@
+#include <stdio.h>
+
+#define MAXNUM 1000
+
+int main(void) {
+  int n;
+  scanf("%d", &n);
+  int maxlen[MAXNUM] = {};
+  int count = 0;
+
+  int prev, head;
+  scanf("%d", &prev);
+  for (int i = 1; i < n; i++) {
+    scanf("%d", &head);
+    if (head == prev) {
+      maxlen[count]++;
+    } else {
+			prev = head;
+			count++;
+		}
+  }
+
+	int max = 1;
+	for (int i = count; i >= 0; i--) {
+		if (maxlen[i] + 1 > max) {
+			max = maxlen[i] + 1;
+		}
+	}
+	printf("%d", max);
+  return 0;
+}