Concise and clear CodeForces - 991F(dfs 有重复元素的全排列)

就是有重复元素的全排列

#include <bits/stdc++.h>
#define mem(a, b) memset(a, b, sizeof(a))
using namespace std;
typedef long long LL;
const int maxn = , INF = 0x7fffffff;
char str[maxn];
int vis[maxn], v[maxn];
LL num[maxn];
LL res = ;
void init()
{
    num[] = ;
    for(int i=; i<maxn; i++)
        num[i] = num[i-] * i;
}
void dfs(LL x, LL cnt)
{
    if(cnt == )
    {
        if(x > ) return;
        LL ans1 = , ans2 = , ans3 = ;
        for(int i=; i<=; i++)
        {
            ans2 += v[i];
        }
        LL temp = ans2;
        ans2 = num[ans2];
        for(int i=; i<=; i++)
            ans2 /= num[v[i]];
    //    cout<< ans2 <<endl;
        if(v[])
        {
            ans3 = num[temp-];
            for(int i=; i<=; i++)
                if(i == ) ans3 /= num[v[i]-];
                else ans3 /= num[v[i]];

            ans2 -= ans3;
        }

        res += ans2;
        return;
    }
    if(!vis[cnt])
        dfs(x, cnt+);
    else
        for(int i=; i<vis[cnt] && i<=x; i++)
        {
            v[cnt] += i;
            dfs(x-i, cnt+);
            v[cnt] -= i;
        }
}
int main()
{
    init();
    cin>> str;
    int len = strlen(str);
    int maxx = -INF;
    LL sum = , ans = , flag = ;
    for(int i=; i<len; i++)
    {
        if(i != )
            if(str[i] != str[i-])
                flag = ;
        vis[str[i]-'']++;
        if(vis[str[i]-''] == ) ans++;
    }
    if(!flag)
    {
        cout<< len <<endl;
        return ;
    }
    res += num[ans];
    if(vis[])
        res -= num[ans-];
    for(int i=; i<=; i++)
        if(vis[i])
            sum += vis[i]-;
    for(int i=; i<=sum; i++)
    {
        for(int i=; i<=; i++)
            if(vis[i])
                v[i] = ;
            else
                v[i] = ;
        dfs(i, );

    }
    cout<< res <<endl;

    return ;
}