Java implementation of the Blue Bridge Cup determinant calculation algorithm to improve

Questions determinant calculation algorithm to improve

Resource constraints
Time limit: 1.0s memory limit: 256.0MB
Problem Description
　　// reportedly the subject of a lot of people have a lot of nonsense, the silly nonsense × not here.
　　Given an N × N matrix A, find | A |.
The input format
　　of the first line of a positive integer N.
　　Next N lines of N integers, the i-th row and j th number indicates A [i] [j].
Output format
　　line, the output of | A |.
Sample input
2
. 1 2
. 3. 4
sample output
-2
size of the data and agreed
　　0 <N≤6
　　-10≤A [I] [J] ≦ 10

PS: This question is difficult mathematical algorithm is not difficult

package com.company;

import java.util.Scanner;

public class 计算行列式 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int [] [] num = new int[n][n];
        for (int i=0;i<n;i++){
            for (int j=0;j<n;j++){
                num[i][j]=sc.nextInt();
            }
        }
        System.out.println(f(num,n));
    }
    public static int f(int num[][],int n){
        if(n==1) return num[0][0];
        if(n==2) return num[0][0]*num[1][1]-num[0][1]*num[1][0];
        int ans = 0;
        int tmp[][] =new int[8][8];
        for(int i=0;i<n;++i)
        {
            for(int row=0; row<n-1; ++row)
            {
                for(int col=0; col<i; ++col)
                    tmp[row][col] = num[row+1][col];
                for(int col=i; col<n-1;++col)
                    tmp[row][col] = num[row+1][col+1];
            }
            ans += num[0][i]*f(tmp,n-1)*(i%2==0?1:-1);
        }
        return ans;
    }
}