Submission #6425174

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Source Code Expand

using System;
using System.Linq;//リストの使用
using System.Collections.Generic;
using System.Text;//テキストの高速出力に必要
class Program
{
	static void Main()
	{
    long mod = 1000000007;
		string[] input = Console.ReadLine().Split(' ');
		int n = int.Parse(input[0]);
		int k = int.Parse(input[1]);
    long[] dp = new long[n];
    long[] sums = new long[n];
    dp[0] = 1;
    dp[1] = 0;
    sums[0] = 1;
    sums[1] = 1;
    long answer = 0;

    for(int i = 2; i <= n-1; i++)
    {
      dp[i] = sums[i-1];
      if(0 <= i-k-1) dp[i] -= sums[i-k-1];
      dp[i] %= mod;
      if(dp[i] < 0) dp[i] += mod;

      sums[i] = sums[i-1] + dp[i];
      sums[i] %= mod;
    }

    answer = sums[n-1];
    if(0 <= n-k) answer -= sums[n-k];
    answer %= mod;
    if(answer < 0) answer += mod;

		Console.WriteLine(answer);
	}
}

Submission Info

Judge Result