備忘録
問題
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。。。