HDU 5787 K-wolf Number（数位DP）

#include <cstdio>
#include <algorithm>
#include <cstring> 
using namespace std;
typedef long long ll;
const int N=25,M=10005;
int bit[N],pw[5],k;
ll dp[N][M][2][2],l,r;
ll DP(int d,int x,bool f,bool lim){
    int c[5];
    if(d==-1)return 1;
    ll &ret=dp[d][x][f][lim];
    if(~ret)return ret; ret=0;
    int st=k-1,y=x,pos=0;
    for(int i=0;i<k;i++)c[i]=y%10,y/=10;
    if(!f){while(!c[st]&&st>=0)st--;}
    for(int i=st;i>=0;i--)pos|=1<<c[i];
    int up=lim?bit[d]:9;
    for(int i=0;i<=up;i++){
        if(pos>>i&1)continue;
        if(f)ret+=DP(d-1,(x-pw[k-1]*c[k-1])*10+i,f,lim&&i==up);
        else if(st==-1&&!i)ret+=DP(d-1,0,0,lim&&i==up);
        else ret+=DP(d-1,x*10+i,st==k-2,lim&&i==up);
    }return ret;
}
ll Cal(ll x){
    if(!x)return 1;int cnt=0;
    while(x)bit[cnt++]=x%10,x/=10;
    memset(dp,-1,sizeof(dp));
    return DP(cnt-1,0,0,1);
}
int main(){
    for(int i=pw[0]=1;i<5;i++)pw[i]=pw[i-1]*10;
    while(~scanf("%lld%lld%d",&l,&r,&k)){
        k--;printf("%lld\n",Cal(r)-Cal(l-1));
    }return 0;
}