Submission #3417337

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Source Code Expand

#include<bits/stdc++.h>
#define LL long long
using namespace std;
const int N = 2e5 + 10;
const int M = 4005;
const int mod = 1e9 + 7;

int n, m, a[N], b[N];
LL inv[M << 1], fac[M << 1], fav[M << 1], dp[M][M];

void init() {
	fac[0] = fav[0] = 1;
	inv[1] = fac[1] = fav[1] = 1;
	for (int i = 2; i < M << 1; ++i) {
		inv[i] = -mod / i * inv[mod % i] % mod + mod;
		fac[i] = fac[i - 1] * i % mod;
		fav[i] = fav[i - 1] * inv[i] % mod;
	}
}

inline void Add(LL &x, LL y) {
	x += y;
	if (x >= mod) x -= mod;
}

inline LL C(int x, int y) {
	if (x < 0 || x < y) return 0;
	return fac[x] * fav[y] % mod * fav[x - y] % mod;
}

int main() {
	init();
	scanf("%d", &n);
	for (int i = 1; i <= n; ++i) {
		scanf("%d%d", &a[i], &b[i]);
		dp[-a[i] + 2001][-b[i] + 2001]++;
	}
	for (int i = 1; i < M - 1; ++i) {
		for (int j = 1; j < M - 1; ++j) {
			Add(dp[i][j + 1], dp[i][j]);
			Add(dp[i + 1][j], dp[i][j]);
		}
	}
	LL ans = 0;
	for (int i = 1; i <= n; ++i) {
		Add(ans, dp[a[i] + 2001][b[i] + 2001]);
		ans -= C(a[i] * 2 + b[i] * 2, a[i] * 2);
		if (ans < 0) ans += mod;
	}
	cout << ans * (mod + 1) / 2 % mod << endl;
	return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:33:17: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &n);
                 ^
./Main.cpp:35:30: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &a[i], &b[i]);
                              ^

Judge Result