Submission #1084219

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Source Code Expand

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <map>
#include <queue>
#include <set>
#include <cmath>
#include <list>
#include <cassert>

using namespace std;

#define y1 roman_kaban
#define rank oryshych_konb
#define ull unsigned long long
const int mod = int(1e9) + 7;
const long long infLL = 2e18;
const int MX = 2061;
int dp[MX][MX];
int main()
{
    //init();
    //cerr << delta << endl;
    //freopen("/Users/ozzy/Documents/in.txt","r", stdin);
    ios_base::sync_with_stdio(false);
    int n, k;
    cin >> n >> k;
    dp[0][n + 1] = 1;
    for(int i = 1; i < k; i++){
        for(int j = n - i + 1; j > 1; j--){
            if(j == n - i + 1) dp[i][j] = (dp[i - 1][j] + dp[i - 1][j + 1]) % mod; else
                            dp[i][j] = (dp[i - 1][j] + dp[i][j + 1]) % mod;
        }
    }
    int ans = 0;
    for(int j = 1; j <= n; j++){
        ans += dp[k - 1][j];
        ans %= mod;
    }
    if(k == 1) ans = 1;
    for(int i = 0; i < n - k - 1; i++){
        ans *= 2;
        ans %= mod;
    }
    cout << ans << endl;
    return 0;
}

Submission Info

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