diff --git a/medium/count_the_hidden_sequences.py b/medium/count_the_hidden_sequences.py
new file mode 100644
index 0000000..3f8fa0e
--- /dev/null
+++ b/medium/count_the_hidden_sequences.py
@@ -0,0 +1,19 @@
+# https://leetcode.com/problems/count-the-hidden-sequences
+
+from typing import List
+
+class Solution:
+    def numberOfArrays(self, differences: List[int], lower: int, upper: int) -> int:
+        total = 0
+        min_sum = 0
+        max_sum = 0
+        for diff in differences:
+            total += diff
+            min_sum = min(min_sum, total)
+            max_sum = max(max_sum, total)
+
+        min_start = lower - min_sum
+        max_start = upper - max_sum
+
+        return max(0, max_start - min_start + 1)
+