P2455 [SDOI2006]线性方程组 题解

乱搞思路

他卡我顺序，那我打乱不就行了嘛

我直接一个 rand()，不断的交换就行了。

交了 \(10\) 遍才过。

/*
	Work by: TLE_Automation
*/
#include<cmath>
#include<queue>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define LL long long
#define int long long
using namespace std;

const int N = 1e6 + 10;
const int MAXN = 2e5 + 10;

inline char readchar() {
	static char buf[100000], *p1 = buf, *p2 = buf;
	return p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, 100000, stdin), p1 == p2) ? EOF : *p1++;
}

inline int read() {
#define readchar getchar
	int res = 0, f = 0;char ch = readchar();
	for(; !isdigit(ch); ch = readchar()) if(ch == '-') f = 1;
	for(; isdigit(ch); ch = readchar()) res = (res << 1) + (res << 3) + (ch ^ '0');
	return f ? -res : res;
}

inline void print(int x) {
	if (x < 0 ) putchar('-'), x = -x;
	if (x > 9 ) print(x / 10);
	putchar(x % 10 + '0');
}

double a[102][102];
int n;

void Gauss() {	
	for(int i = 1; i <= n; i++) {
		int Max = i;
		for(int j = i + 1; j <= n; j++) if(fabs(a[j][i]) > fabs(a[Max][i])) Max = j;
		for(int j = 1; j <= n + 1; j++) swap(a[i][j], a[Max][j]);
		if(a[i][i] == 0) continue;
		for(int j = 1; j <= n; j++) {
			if(j == i) continue;
			double tmp = a[j][i] / a[i][i];
			for(int k = 1; k <= n + 1; k++) a[j][k] -= a[i][k] * tmp; 
		}
	}
}

#include<ctime>

signed main() {
	srand(time(0));
	n = read();
	for(int i = 1; i <= n; i++) {
		for(int j = 1; j <= n + 1; j++) {
			scanf("%lf", &a[i][j]);
		}
	}
	int T = 10;
	while(T--) {
		for(int i = 1; i <= n; i++) {
			int rd = rand() % n + 1;
			for(int j = 1; j <= n + 1; j++) {
				swap(a[i][j], a[rd][j]);
			}
		}
	}
	Gauss();
	for(int i = 1; i <= n; i++) {
		if(a[i][i] == 0 && a[i][n + 1] == 0) return puts("0"), 0;
		if(a[i][i] == 0 && a[i][n + 1] != 0) return puts("-1"), 0;
	}
	for(int i = 1; i <= n; i++) {
		printf("x%lld=%.2lf\n", i, a[i][n + 1] / a[i][i]);
	}
}