Submission #808731

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Source Code Expand

#include <iostream>
#include <memory>
#include <vector>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <array>
#include <sstream>

using namespace std;

uint64_t perm(int n, int m);
uint64_t fact(int x);

int main(int argc, const char * argv[]) {
    int N;
    vector<pair<int, int>> sks;
    
    uint64_t sum = 0;
    
    cin >> N;
    
    for (int i = 0; i < N; i++) {
        string t1, t2;
        cin >> t1 >> t2;
        sks.push_back(make_pair(atoi(t1.c_str()), atoi(t2.c_str())));
    }
    
    for (int i = 0; i < N; i++) {
        for (int j = i + 1; j < N; j++) {
            int meat = sks[i].first + sks[j].first;
            int veg = sks[i].second + sks[j].second;
            int u = meat + veg;
            int d = max(meat, veg);
            sum += perm(u, u - d) / fact(min(meat, veg));
        }
    }
    
    cout << sum % (1000000007) << endl;
    
    return 0;
}

uint64_t perm(int n, int m) {
    uint64_t v = 1;
    for (uint64_t i = 0; i < m; i++) v *= (n - i);
    return v;
}
uint64_t fact(int x) {
    static map<int, uint64_t> memo;
    if (memo.find(x) != memo.end()) return memo[x];
    uint64_t v = 1;
    for (uint64_t i = 1; i <= x; i++) v *= i;
    memo[x] = v;
    return v;
}

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