URAL 2052 Physical Education（数位DP）

题目链接：https://vjudge.net/contest/254142#problem/G

参考题解：https://blog.csdn.net/zearot/article/details/47984379

 #include <bits/stdc++.h>
 using namespace std;
 #define ll long long
 #define LL __int128
 #define ull unsigned long long
 #define mst(a,b) memset((a),(b),sizeof(a))
 #define mp(a,b) make_pair(a,b)
 #define pi acos(-1)
 #define pii pair<int,int>
 #define pb push_back
 const int INF = 0x3f3f3f3f;
 const double eps = 1e-;
 const int MAXN = 1e5 + ;
 const int MAXM = 2e6 + ;
 const ll mod = 1e9 + ;

 int f[][], dig[];

 void init() {
     mst(f, );
     f[][] = ;
     for(int i = ; i <= ; i++)
         for(int j = ; j <= i * ; j++)
             for(int k = ; k <= min(, j); k++)
                 f[i][j] += f[i - ][j - k];
 }

 int findall(int pos,int sum,bool limit) {
     if(!limit || !pos) return f[pos][sum];
     int ans = , mx = min(dig[pos], sum);
     for(int i = ; i <= mx; i++)
         ans += findall(pos - ,sum - i,limit && i == dig[pos]);
     return ans;
 }

 int shu[];

 void findd(int pos,int sum,int rnk,bool limit) {
     if(!pos) return ;
     if(!limit) {
         int mx = min(, sum);
         for(int i = ; i <= mx; i++) {
             if(f[pos - ][sum - i] < rnk) rnk -= f[pos - ][sum - i];
             else {
                 shu[pos] = i;
                 findd(pos - ,sum - i,rnk,limit);
                 return ;
             }
         }
     } else {
         int mx = min(dig[pos], sum);
         for(int i = ; i <= mx; i++) {
             int temp = findall(pos - ,sum - i,i == dig[pos]);
             if(temp < rnk) rnk -= temp;
             else {
                 shu[pos] = i;
                 findd(pos - ,sum - i,rnk,i == dig[pos]);
                 return ;
             }
         }
     }
 }

 int main()
 {
 #ifdef local
     freopen("data.txt", "r", stdin);
 //    freopen("data.txt", "w", stdout);
 #endif
     init();
     int n,len = ;
     scanf("%d",&n);
     while(n) {
         dig[++len] = n % ;
         n /= ;
     }
     int ans = ,sum = ;
     for(int i = ; i <= len * ; i++) {
         int num = findall(len,i,true);
         if(!num) continue;
         int l = , r = num, num1;
         bool flag = false;
         while(l <= r) {
             int mid = (l + r) >> ;
             findd(len,i,mid,true);
             num1 = ;
             for(int j = len; j >= ; j--) {
                 if(!num1 && !shu[j]) continue;
                 num1 = num1 *  + shu[j];
             }
             if(sum + mid > num1) l = mid + ;
             else if(sum + mid < num1) r = mid - ;
             else {
                 flag = true;
                 break;
             }
         }
         if(flag) ans++;
         sum += num;
     }
     printf("%d\n",ans);
     return ;
 }