diff --git a/sean/class4-2/11660.py b/sean/class4-2/11660.py
new file mode 100644
index 0000000..f82bf71
--- /dev/null
+++ b/sean/class4-2/11660.py
@@ -0,0 +1,23 @@
+import sys
+
+# sys.stdin = open("input.txt", "r")
+
+n, m = map(int, input().split())
+
+arr = [list(map(int, input().split())) for _ in range(n)]
+
+sum_arr = [[0] * n for _ in range(n)]
+
+for i in range(0, n):
+    for j in range(n):
+        prev_row = sum_arr[i - 1][j] if (i != 0) else 0
+        prev_col = sum_arr[i][j - 1] if (j != 0) else 0
+        prev_sum = sum_arr[i - 1][j - 1] if (i != 0 and j != 0) else 0
+        sum_arr[i][j] = arr[i][j] + prev_row + prev_col - prev_sum
+
+for _ in range(m):
+    x1, y1, x2, y2 = map(lambda x: int(x) - 1, input().split())
+    prev_row = sum_arr[x1 - 1][y2] if (x1 != 0) else 0
+    prev_col = sum_arr[x2][y1 - 1] if (y1 != 0) else 0
+    prev_sum = sum_arr[x1 - 1][y1 - 1] if (x1 != 0 and y1 != 0) else 0
+    print(sum_arr[x2][y2] - prev_row - prev_col + prev_sum)
diff --git a/sean/class4-2/12865.py b/sean/class4-2/12865.py
new file mode 100644
index 0000000..c368682
--- /dev/null
+++ b/sean/class4-2/12865.py
@@ -0,0 +1,22 @@
+import sys
+
+# sys.stdin = open("input.txt", "r")
+
+n, k = map(int, input().split())
+
+items = sorted(
+    [list(map(int, input().split())) for _ in range(n)],
+    key=lambda x: x[1] / x[0],
+    reverse=True,
+)
+
+dp = [0] * (k + 1)
+
+answer = 0
+for weight, price in items:
+    for i in range(k, weight - 1, -1):
+        if i - weight >= 0:
+            dp[i] = max(dp[i], dp[i - weight] + price)
+            answer = max(answer, dp[i])
+
+print(answer)
diff --git a/sean/class4-2/13549.py b/sean/class4-2/13549.py
new file mode 100644
index 0000000..d81f597
--- /dev/null
+++ b/sean/class4-2/13549.py
@@ -0,0 +1,27 @@
+from collections import deque
+import sys
+
+# sys.stdin = open("input.txt", "r")
+
+n, k = map(int, input().split())
+
+MAX_POS = 200000
+
+dp = [MAX_POS + 1] * (MAX_POS + 1)
+
+queue = deque([n])
+dp[n] = 0
+
+while queue:
+    x = queue.popleft()
+    if x != 0 and dp[x - 1] > dp[x] + 1:
+        dp[x - 1] = dp[x] + 1
+        queue.append(x - 1)
+    if x + 1 <= MAX_POS and dp[x + 1] > dp[x] + 1:
+        dp[x + 1] = dp[x] + 1
+        queue.append(x + 1)
+    if 2 * x <= MAX_POS and dp[2 * x] > dp[x]:
+        dp[2 * x] = dp[x]
+        queue.append(2 * x)
+
+print(dp[k])
diff --git a/sean/class4-2/1753.py b/sean/class4-2/1753.py
new file mode 100644
index 0000000..7b3ecce
--- /dev/null
+++ b/sean/class4-2/1753.py
@@ -0,0 +1,33 @@
+import heapq
+import sys
+
+# sys.stdin = open("input.txt", "r")
+
+v, e = map(int, input().split())
+k = int(input())
+
+
+graph = {i: [] for i in range(1, v + 1)}
+for i in range(e):
+    _u, _v, _w = map(int, input().split())
+    graph[_u].append((_v, _w))
+
+distance = [float("inf")] * (v + 1)
+distance[k] = 0
+
+pq = []
+heapq.heappush(pq, (0, k))
+
+while pq:
+    _w, cur = heapq.heappop(pq)
+
+    if _w > distance[cur]:
+        continue
+
+    for next, weight in graph[cur]:
+        next_weight = _w + weight
+        if next_weight < distance[next]:
+            distance[next] = next_weight
+            heapq.heappush(pq, (next_weight, next))
+
+print("\n".join(map(lambda x: str(x) if x != float("inf") else "INF", distance[1:])))
diff --git a/sean/class4-2/1967.py b/sean/class4-2/1967.py
new file mode 100644
index 0000000..cdce496
--- /dev/null
+++ b/sean/class4-2/1967.py
@@ -0,0 +1,30 @@
+from collections import deque
+import sys
+
+# sys.stdin = open("input.txt", "r")
+
+n = int(input())
+
+tree = [[] for _ in range(n + 1)]
+
+for _ in range(n - 1):
+    a, b, c = map(int, input().split())
+    tree[a].append((b, c))
+    tree[b].append((a, c))
+
+answer = 0
+for root in range(1, n + 1):
+    visited = [-1] * (n + 1)
+    visited[root] = 0
+
+    queue = deque([root])
+    while queue:
+        cur = queue.popleft()
+
+        for next, weight in tree[cur]:
+            if visited[next] == -1:
+                visited[next] = visited[cur] + weight
+                queue.append(next)
+                answer = max(answer, visited[next])
+
+print(answer)
diff --git a/sean/class4-2/9251.py b/sean/class4-2/9251.py
new file mode 100644
index 0000000..19802d2
--- /dev/null
+++ b/sean/class4-2/9251.py
@@ -0,0 +1,22 @@
+import sys
+
+# sys.stdin = open("input.txt", "r")
+
+sequence = [input(), input()]
+
+sequence_table = [[0] * (len(sequence[1]) + 1) for _ in range(len(sequence[0]) + 1)]
+
+
+answer = 0
+for i in range(1, len(sequence[0]) + 1):
+    for j in range(1, len(sequence[1]) + 1):
+        if sequence[0][i - 1] == sequence[1][j - 1]:
+            prev = sequence_table[i - 1][j - 1] if (i != 0 and j != 0) else 0
+            sequence_table[i][j] = prev + 1
+        else:
+            prev_row = sequence_table[i - 1][j] if (i != 0) else 0
+            prev_col = sequence_table[i][j - 1] if (j != 0) else 0
+            sequence_table[i][j] = max(prev_row, prev_col)
+        answer = max(answer, sequence_table[i][j])
+
+print(answer)
\ No newline at end of file
diff --git a/sean/class4-2/9663.py b/sean/class4-2/9663.py
new file mode 100644
index 0000000..1eeb6c7
--- /dev/null
+++ b/sean/class4-2/9663.py
@@ -0,0 +1,26 @@
+import sys
+
+# sys.stdin = open("input.txt", "r")
+
+n = int(input())
+
+
+def n_queen(row, col, sum, diff):
+    if row == n:
+        return 1
+
+    ret = 0
+    for j in range(0, n):
+        if col[j] or sum[row + j] or diff[row - j + n]:
+            continue
+        col[j] = True
+        sum[row + j] = True
+        diff[row - j + n] = True
+        ret = ret + n_queen(row + 1, col, sum, diff)
+        col[j] = False
+        sum[row + j] = False
+        diff[row - j + n] = False
+    return ret
+
+
+print(n_queen(0, [False] * n, [False] * (2 * n), [False] * (2 * n)))