行列式值计算

	int x, y;
	
	int exGCD(int a, int b) {
		if (0 == b) {
			x = 1; y = 0;
			return a;
		}
		int r = exGCD(b, a % b);
		int t = x; 
		x = y;
		y = t - a / b * y;
		return r;
	}

	int det(int n) { // n: n行n列
		int ans = 1;
		boolean flag = true; // 行交换次数奇偶
		for (int i = 0, j, k; i < n; ++i) {
			if (0 == C[i][i]) {
				for (j = i + 1; j < n; ++j)
					if (C[j][i] > 0) break;
				if (j >= n) return 0; // 整个行列式的值为0
				flag = !flag;
				for (k = i; k < n; ++k) {
					int temp = C[i][k];
					C[i][k] = C[j][k];
					C[j][k] = temp;
				}
			}
			ans = ans * C[i][i] % MOD;
			exGCD(C[i][i], MOD); // 求C[i][j]的乘法逆元
			x = (x + MOD) % MOD;
			for (k = i + 1; k < n; ++k) 
				C[i][k] = C[i][k] * x % MOD;
			for (j = i + 1; j < n; ++j) {
				if (0 != C[j][i]) {
					for (k = i + 1; k < n; ++k) 
						C[j][k] = ((C[j][k] - C[i][k] * C[j][i] % MOD + MOD) % MOD);
				}
			}
		}
		if (flag) return ans;
		return MOD - ans;
	}