Create triangle.py

data_structures/queues/design_hit_counter.py

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+from collections import deque
+
+
+class HitCounter:
+    """
+    A counter that records hits (events) and can return
+    the number of hits in the past 5 minutes (300 seconds).
+
+    >>> hc = HitCounter()
+    >>> hc.hit(1)
+    >>> hc.hit(2)
+    >>> hc.hit(300)
+    >>> hc.get_hits(300)
+    3
+    >>> hc.get_hits(301)
+    2
+    """
+
+    def __init__(self) -> None:
+        self.hits: deque[int] = deque()
+
+    def hit(self, timestamp: int) -> None:
+        """Record a hit at the given timestamp (in seconds)."""
+        self.hits.append(timestamp)
+
+    def get_hits(self, timestamp: int) -> int:
+        """
+        Return the number of hits in the past 5 minutes
+        from the given timestamp.
+        """
+        while self.hits and self.hits[0] <= timestamp - 300:
+            self.hits.popleft()
+        return len(self.hits)
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()

dynamic_programming/triangle.py

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+from __future__ import annotations
+
+
+def minimum_total(triangle: list[list[int]]) -> int:
+    """
+    Return the minimum path sum from top to bottom of a triangle.
+
+    Each step you may move to adjacent numbers on the row below.
+    The input must be a proper triangle: len(row i) == i + 1.
+
+    >>> minimum_total([[2],[3,4],[6,5,7],[4,1,8,3]])
+    11
+    >>> minimum_total([[-10]])
+    -10
+    >>> minimum_total([[1],[2,3]])
+    3
+    >>> minimum_total([])  # doctest: +IGNORE_EXCEPTION_DETAIL
+    Traceback (most recent call last):
+    ValueError: triangle must be non-empty and well-formed
+    >>> minimum_total([[1],[2]])  # doctest: +IGNORE_EXCEPTION_DETAIL
+    Traceback (most recent call last):
+    ValueError: triangle must be non-empty and well-formed
+    """
+    # Basic validation: non-empty and proper "triangle" shape
+    if not triangle or any(len(row) != i + 1 for i, row in enumerate(triangle)):
+        raise ValueError("triangle must be non-empty and well-formed")
+
+    # Start from the last row and fold upwards. dp[j] stores the minimum path
+    # sum from row r to the bottom starting at column j.
+    dp = triangle[-1][:]  # copy so we don't mutate the input
+
+    for r in range(len(triangle) - 2, -1, -1):
+        for c in range(r + 1):
+            dp[c] = triangle[r][c] + min(dp[c], dp[c + 1])
+
+    return dp[0]
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()