蓝桥杯--算法提高 最大乘积(DFS)

Problem

对于n个数，从中取出m个数，如何取使得这m个数的乘积最大呢？

Solution

数据规模不大，直接DFS穷举每一种组合，计算最大乘积。

# include 
# include 
# include 
using namespace std;

const int maxn = 20;
int n, m;
int a[maxn], b[maxn], used[maxn];
int ans;


void dfs(int pos)
{
    if(pos == m){
        int product = 1;
        for(int i = 0; i < m; ++i){
            product *= b[i];
        }
        if(ans < product)
            ans = product;
        return;
    }

    for(int i = 0; i < n; ++i)
    {
        if(!used[i])
        {
            b[pos] = a[i];
            used[i] = true;
            dfs(pos + 1);
            used[i] = false;
        }
    }
}


int main()
{
    //freopen("data.in", "r", stdin);
    int test;

    cin >> test;
    while(test--)
    {
        cin >> n >> m;
        ans = -0xFFFF;
        memset(b, 0, sizeof(b));
        memset(used, 0, sizeof(used));
        for(int i = 0; i < n; ++i)
            cin >> a[i];

        dfs(0);
        cout << ans << endl;
    }
}