HDU 2827 高斯消元

模板的高斯消元....

/** @Date    : 2017-09-26 18:05:03
  * @FileName: HDU 2827 高斯消元.cpp
  * @Platform: Windows
  * @Author  : Lweleth (SoungEarlf@gmail.com)
  * @Link    : https://github.com/
  * @Version : $Id$
  */
#include <bits/stdc++.h>
#define LL long long
#define PII pair
#define MP(x, y) make_pair((x),(y))
#define fi first
#define se second
#define PB(x) push_back((x))
#define MMG(x) memset((x), -1,sizeof(x))
#define MMF(x) memset((x),0,sizeof(x))
#define MMI(x) memset((x), INF, sizeof(x))
using namespace std;

const int INF = 0x3f3f3f3f;
const int N = 1e5+20;
const double eps = 1e-8;

LL a[110][110];
LL mod;
int n;

LL gauss(int n)
{
	int last, row;
	LL ans = 1;
	int flag = 0;
	for(int i = 0; i < n; i++)
	{
		for(int j = i + 1; j < n; j++)//从i+1行开始的所有行
		{
			last = i;
			row = j;
			while(a[row][i])//到i列为止都为0
			{
				LL t = a[last][i] / a[row][i];
				for(int k = i; k < n; k++)
				{
					a[last][k] = (a[last][k] % mod - (a[row][k] * t % mod) + mod) % mod;
					while(a[last][k] < 0)
						a[last][k] += mod;
				}
				swap(last, row);//不断交换
			}
			if(last != i)//保证上比下大
			{
				flag++ ;//行基本操作 交换 正负号改变
				for(int k = 0; k < n; k++)
					swap(a[i][k], a[last][k]);
			}
		}
		//cout << a[i][i] << endl;
		if(a[i][i] == 0) //
			return 0;
		else //对角线之积
			ans = (ans * a[i][i] % mod + mod) % mod;
	}
	if(flag % 2)
		ans *= -1;
	while(ans < 0)
		ans += mod;
	return ans;
}

int main()
{
	while(cin >> n >> mod)
	{
		MMF(a);
		for(int i = 0; i < n; i++)
			for(int j = 0; j < n; j++)
				scanf("%lld", &a[i][j]);
		LL ans = gauss(n);
		printf("%lld\n", ans);
	}
    return 0;
}