Submission #4476794

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Source Code Expand

#include<iostream>
#include<algorithm>
#include<vector>
#include<queue>
#include<map>
#include<set>
#include<string>
#include<stack>
#include<cstdio>
#include<cmath>
using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int,int> P;
typedef pair<int,P> P1;

#define fr first
#define sc second
#define mp make_pair
#define pb push_back
#define rep(i,x) for(int i=0;i<x;i++)
#define rep1(i,x) for(int i=1;i<=x;i++)
#define rrep(i,x) for(int i=x-1;i>=0;i--)
#define rrep1(i,x) for(int i=x;i>0;i--)
#define sor(v) sort(v.begin(),v.end())
#define rev(s) reverse(s.begin(),s.end())
#define lb(vec,a) lower_bound(vec.begin(),vec.end(),a)
#define ub(vec,a) upper_bound(vec.begin(),vec.end(),a)
#define uniq(vec) vec.erase(unique(vec.begin(),vec.end()),vec.end())
#define mp1(a,b,c) P1(a,P(b,c))

const int INF=1000000000;
const int dir_4[4][2]={{1,0},{0,1},{-1,0},{0,-1}};
const int dir_8[8][2]={{1,0},{1,1},{0,1},{-1,1},{-1,0},{-1,-1},{0,-1},{1,-1}};

const ll M = 1000000007;

int main(){
	ll n,m,k;
	cin >> n >> m >> k;
	
	ll ret = 0;
	ll dp[2002] = {};
	rep1(i,k-1)dp[i] = 1;
	rep1(t,400000){
		if(t*k-(t-1)-m > n)break;
		//cout << t << endl;
		/*rep(i,m+1){
			cout << dp[i] << " ";
		}cout << endl;*/
		for(int i = m ; i >= 1 && t*k-(t-1)-i <= n ; i -= k-1){
			ret += dp[i];
			if(ret >= M)ret -= M;
		}
		ll sum = 0;
		rep(i,k){
			if(m-i < 0)break;
			sum += dp[m-i];
		}
		sum %= M;
		//cout << sum << endl;
		rrep(i,m+1){
			sum += M-dp[i];
			dp[i] += sum;
			dp[i] %= M;
			if(i-k >= 0)sum += dp[i-k];
			sum %= M;
		}
	}
	cout << ret << endl;
}

Submission Info

Judge Result