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Problem solution · Python

ABC435 E — Cover query

ABC435 E — Cover query: a Python solution using sliding window or two pointers. Learn the idea, check the complexity, and read the full code, with credit to KATO-Hiro AtCoder Solutions.

Technique
Sliding window or two pointers
Source
KATO-Hiro AtCoder Solutions
Length
66 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Sliding window or two pointers

For ABC435 E — Cover query, the implementation maintains a moving interval and updates only the information that enters or leaves the window.

  1. Choose the invariant that makes a window valid or useful.
  2. Advance the right boundary and add the new element.
  3. Move the left boundary only as needed while maintaining the invariant and updating the answer.

Code notes

  • 66 lines of Python from the credited upstream file abc435_e.py.
  • The implementation visibly relies on sequence storage, ordered lookup.
  • No explicit loop blocks detected.

Complexity

Confirm that neither pointer moves backwards; if so, the scan is usually linear apart from the window’s data-structure operations.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from KATO-Hiro AtCoder Solutions by KATO-Hiro and is used under the CC0-1.0 licence.

Open problem ↗Original source ↗
Full codeABC435 E — Cover query · PythonPython
Use this to learn the idea, then write your own version.
# -*- coding: utf-8 -*- from bisect import bisect_left  def bisect_ge(sorted_array: list[int], value: int):    """Find the smallest element >= x and its index, or None if it doesn't exist."""     if sorted_array[-1] >= value:        index: int = bisect_left(sorted_array, value)         return index, sorted_array[index]     return None, None  def main():    import sys    from itertools import pairwise    from atcoder.lazysegtree import LazySegTree  # type: ignore     input = sys.stdin.readline     n, q = map(int, input().split())    lr = [tuple(map(int, input().split())) for _ in range(q)]    compressed = set([0, n])     for li, ri in lr:        compressed.add(li - 1)        compressed.add(ri)     compressed = sorted(compressed)    # cell_count, node_count    counts = [(second - first, 1) for first, second in pairwise(compressed)]     def op(a, b):        return (a[0] + b[0], a[1] + b[1])     e = (0, 0)     pending = -1     def mapping(f, a):        return a if f == pending else (f * a[1], a[1])     def composition(f, g):        return g if f == pending else f     id = pending     st = LazySegTree(op, e, mapping, composition, id, counts)     for li, ri in lr:        li -= 1         left, _ = bisect_ge(compressed, li)        right, _ = bisect_ge(compressed, ri)        st.apply(left, right, 0)         ans = st.all_prod()[0]        print(ans)  if __name__ == "__main__":    main()

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