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mirror of https://git.sb/baoshuo/OI-codes.git synced 2024-12-24 03:31:59 +00:00

P2455 [SDOI2006]线性方程组

https://www.luogu.com.cn/record/89160212
This commit is contained in:
Baoshuo Ren 2022-10-08 18:39:59 +08:00
parent 1735d32222
commit 7d55593096
Signed by: baoshuo
GPG Key ID: 00CB9680AB29F51A

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Luogu/P2455/P2455.cpp Normal file
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#include <iostream>
#include <iomanip>
using std::cin;
using std::cout;
const char endl = '\n';
const int N = 55;
const double eps = 1e-6;
int n;
double a[N][N];
int gauss() {
int r, c;
for (r = c = 1; c <= n; c++) {
int t = r;
for (int i = r; i <= n; i++) {
if (std::abs(a[i][c]) > std::abs(a[t][c])) t = i;
}
if (std::abs(a[t][c]) < eps) continue;
std::swap(a[t], a[r]);
for (int i = n + 1; i >= c; i--) {
a[r][i] /= a[r][c];
}
for (int i = r + 1; i <= n; i++) {
if (std::abs(a[i][c]) > eps) {
for (int j = n + 1; j >= c; j--) {
a[i][j] -= a[i][c] * a[r][j];
}
}
}
r++;
}
if (r <= n) {
for (int i = r; i <= n; i++) {
if (std::abs(a[i][n + 1]) > eps) {
return -1;
}
}
return 1;
}
for (int i = n; i; i--) {
for (int j = i + 1; j <= n; j++) {
a[i][n + 1] -= a[i][j] * a[j][n + 1];
}
}
return 0;
}
int main() {
std::ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= n + 1; j++) {
cin >> a[i][j];
}
}
int r = gauss();
if (r == 1) {
cout << 0 << endl;
} else if (r == -1) {
cout << -1 << endl;
} else {
for (int i = 1; i <= n; i++) {
cout << 'x' << i << '=' << std::fixed << std::setprecision(2) << (std::abs(a[i][n + 1]) < eps ? 0.0 : a[i][n + 1]) << endl;
}
}
return 0;
}