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http://acm.hdu.edu.cn/showproblem.php?pid=2062
Time Limit: 1000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 3569    Accepted Submission(s): 1802
#include <iostream>
#include <cstring>
using namespace std;
typedef unsigned long long ll;
int n;
ll m;
int bit[20],len;
bool used[21];
int fnd(int ind){
        int ind2=0;
        for(int i=1;i<21;i++){
                if(!used[i]){
                        if(ind==ind2)return i;
                        ind2++;
                }
        }
        return -1;
}
ll all;
ll dis[21];
int main(){
        while(cin>>n>>m){
                memset(used,0,sizeof(used));
                all =1;
                ll sub=1;
                for(int i=0;i<n;i++){
                        sub*=(n-i);
                        all+=sub;
                }
                for(int i=0;i<n;i++){
                        all--;
                        dis[i]=all/(n-i);
                        all/=(n-i);
                }
                len=0;
                for(int i=n;i>=1;i--,len++){
                        if(m==0){break;}
                        m--;
                        bit[len]=fnd(m/dis[len]);
                        used[bit[len]]=true;
                        m%=dis[len];
                }
                for(int i=0;i<len;i++){
                        cout<<bit[i]<<(i==len-1?‘\n‘:‘ ‘);
                }
        }
        return 0;
}
HDU 2062 Subset sequence 数位dp,思路 难度:1
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原文地址:http://www.cnblogs.com/xuesu/p/4296787.html