AtCoder Regular Contest 107 B - Quadruple

備忘録

問題

atcoder.jp

回答

import sys
import os
import math
import bisect
import itertools
import collections
import heapq
import queue
import array
import time
import numpy as np
from numpy import linalg as LA

# 時々使う
# import numpy as np
# from decimal import Decimal, ROUND_HALF_UP
# from scipy.sparse.csgraph import csgraph_from_dense, floyd_warshall
# from collections import defaultdict, deque

# 再帰の制限設定
sys.setrecursionlimit(10000000)


def ii(): return int(sys.stdin.buffer.readline().rstrip())
def il(): return list(map(int, sys.stdin.buffer.readline().split()))
def fl(): return list(map(float, sys.stdin.buffer.readline().split()))
def iln(n): return [int(sys.stdin.buffer.readline().rstrip())
                    for _ in range(n)]


def iss(): return sys.stdin.buffer.readline().decode().rstrip()
def sl(): return list(map(str, sys.stdin.buffer.readline().decode().split()))
def isn(n): return [sys.stdin.buffer.readline().decode().rstrip()
                    for _ in range(n)]


def lcm(x, y): return (x * y) // math.gcd(x, y)


# MOD = 10 ** 9 + 7
MOD = 998244353
INF = float('inf')


def main():
    if os.getenv("LOCAL"):
        sys.stdin = open("input.txt", "r")

    N, K = il()
    ary = [0] * (2 * 10**5 + 1)
    if K < 0:
        # K > 0 または K < 0 でも回答は同じだが、
        # 後続の処理のために K > 0 にする
        K *= -1

    for n in range(2, 2*N+1):
        ary[n] = max(min(n-1, 2 * N + 1 - n), 0)
    ret = 0
    for n in range(K, 2*N+1):
        ret += ary[n] * ary[n-K]
    print(ret)


if __name__ == '__main__':
    main()

考え方

等式の変形させる問題いつも解けない。。。

AtCoder ARC 107 B - Quadruple (茶色, 400 点) - けんちょんの競プロ精進記録

ARC107 – B Quadruple – Sooh31's programming diary