Submission #44212293

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Source Code Expand

// LUOGU_RID: 118885458
#include<bits/stdc++.h>
#define LL long long
#define DB double
#define MOD 1000000007
#define ls(x) x << 1
#define rs(x) x << 1 | 1
#define lowbit(x) x & (-x)
#define PII pair<int, int>
#define MP make_pair
#define VI vector<int>
#define VII vector<int>::iterator
#define all(x) x.begin(), x.end()
#define EB emplace_back
#define SI set<int>
#define SII set<int>::iterator
#define QI queue<int>
using namespace std;
template<typename T> void chkmn(T &a, const T &b) { (a > b) && (a = b); }
template<typename T> void chkmx(T &a, const T &b) { (a < b) && (a = b); }
int inc(const int &a, const int &b) { return a + b >= MOD ? a + b - MOD : a + b; }
int dec(const int &a, const int &b) { return a - b < 0 ? a - b + MOD : a - b; }
int mul(const int &a, const int &b) { return 1LL * a * b % MOD; }
int sqr(const int &a) { return 1LL * a * a % MOD; }
void Inc(int &a, const int &b) { ((a += b) >= MOD) && (a -= MOD); }
void Dec(int &a, const int &b) { ((a -= b) < 0) && (a += MOD); }
void Mul(int &a, const int &b) { a = 1LL * a * b % MOD; }
void Sqr(int &a) { a = 1LL * a * a % MOD; }
int qwqmi(int x, int k = MOD - 2)
{
	int res = 1;
	while(k)
	{
		if(k & 1) Mul(res, x);
		Sqr(x), k >>= 1;
	}
	return res;
}
const int N = 3e3 + 5;
const int inv2 = (MOD + 1) / 2;
int n, Q, a[N];
int f[N][N], ans;
int main()
{
	scanf("%d %d", &n, &Q);
	for(int i = 1; i <= n; ++i)
		scanf("%d", &a[i]);
	for(int i = 1; i <= n; ++i)
		for(int j = 1; j <= n; ++j)
			f[i][j] = (a[i] > a[j]);
	for(int cas = 1; cas <= Q; ++cas)
	{
		int x, y;
		scanf("%d %d", &x, &y);
		if(x > y) swap(x, y);
		f[x][y] = f[y][x] = mul(inc(f[x][y], f[y][x]), inv2);
		for(int i = 1; i <= n; ++i)
		{
			if(i == x || i == y) continue;
			f[x][i] = f[y][i] = mul(inc(f[x][i], f[y][i]), inv2);
			f[i][x] = f[i][y] = mul(inc(f[i][x], f[i][y]), inv2);
		}
	}
	for(int i = 1; i < n; ++i)
		for(int j = i + 1; j <= n; ++j)
			Inc(ans, f[i][j]);
	Mul(ans, qwqmi(2, Q));
	printf("%d\n", ans);
	return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:45:7: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   45 |  scanf("%d %d", &n, &Q);
      |  ~~~~~^~~~~~~~~~~~~~~~~
./Main.cpp:47:8: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   47 |   scanf("%d", &a[i]);
      |   ~~~~~^~~~~~~~~~~~~
./Main.cpp:54:8: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   54 |   scanf("%d %d", &x, &y);
      |   ~~~~~^~~~~~~~~~~~~~~~~

Judge Result