代码

#include <bits/stdc++.h>

#define idx(i, j) ((i) * n + (j))

void matrix_multiply(int n, const double *A, const double *B, double *C) {
	double *BB = reinterpret_cast<double*> (B);
	for (int i = 0; i < n; i++) for (int j = i + 1; j < n; j++) {
		swap(B[idx(i, j)], B[idx(j, i)]);
	}
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			double sum = 0;
			for (int k = 0; k < n; k++) {
				sum += A[idx(i, k)] * BB[idx(j, k)];
			}
			C[idx(i, j)] = sum;
		}
	}
}

评测结果