Submission #1075744

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Source Code Expand

// In the name of God

#include <iostream>
#include <algorithm>
#include <fstream>
#include <vector>
#include <deque>
#include <assert.h>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <stdio.h>
#include <string.h>
#include <utility>
#include <math.h>
#include <bitset>
#include <iomanip>

using namespace std;

const int N = (int) 2005, mod = (int) 1e9 + 7;

int dp[N], odp[N];
void sadd(int &x, int y) { x += y; x %= mod; }
int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int n, m, k, res = 0;
    cin >> n >> m >> k;
    dp[1] = 1;
    for (int h = 1; h <= (n + m + 2200) / (k - 1); ++h) {
        int val = h * (k - 1) + 1;
        memcpy(odp, dp, sizeof dp);
        memset(dp, 0, sizeof dp);
        for (int last = 0; last <= n; ++last) for (int j = 0; j < k && last + j <= n; ++j) {
            sadd(dp[last + j], odp[last]);
        }
        if (val % (k - 1) == (n + m) % (k - 1)) {
            for (int j = 1; j <= n; ++j)
                if (val - j <= m && j % (k - 1) == n % (k - 1)) {
                    //cout << h << ' ' << j << ' ' << dp[j] << ' ' << val << ' ' << val - j << endl;
                    sadd(res, (dp[j] - (j - k + 1 >= 0? odp[j - k + 1]: 0) + mod) % mod);
                }
        }
    }
    cout << res << endl;
}

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