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[1024 * 1024];
	memcpy(BB, B, sizeof(double) << 20);
	for (int i = 0; i < n; i++) for (int j = i + 1; j < n; j++) {
		std::swap(BB[idx(i, j)], BB[idx(j, i)]);
	}
}

评测结果