【DFS】AcWing842. 排列数字

AcWing842.排列数字

题解

#include <iostream>

using namespace std;

const int N = 10;

bool vis[N];
int nums[N], n;

void dfs(int u)
{
    if(u == n + 1) 
    {
        for(int i = 1; i <= n; ++i) printf("%d ",nums[i]);
        puts("");
        return;
    }
    for(int i = 1; i <= n; ++i)
        if(!vis[i])
        {
            nums[u] = i;
            vis[i] = true;
            dfs(u + 1);
            vis[i] = false;
        }
}

int main()
{
    scanf("%d",&n);
    dfs(1);
    return 0;
}

通过位操作优化标记数组：

#include <iostream>

using namespace std;

const int N = 10;

int nums[N], n;

void dfs(int u, int state)
{
    if(u == n + 1) 
    {
        for(int i = 1; i <= n; ++i) printf("%d ",nums[i]);
        puts("");
        return;
    }
    for(int i = 1; i <= n; ++i)
        if( !(state >> i & 1) )
        {
            nums[u] = i;
            state += 1 << i;
            dfs(u + 1, state);
            state -= 1 << i;
        }
}

int main()
{
    scanf("%d",&n);
    dfs(1, 0);
    return 0;
}