ural1057 Amount of degrees 位数统计

 #include <iostream>
 #include <string>
 using namespace std;

 int f[][];
 void init(){
     f[][] =;
     for(int i=;i<=;i++){
         f[i][] = f[i-][];
         for(int j=;j<=i;j++)
             f[i][j] = f[i-][j]+f[i-][j-];
     }
 }

 int change(int x,int b){
     string s;
     while(x){
         s = (char)(x%b+'')+s;
         x = x/b;
     }
     for(int i=;i<s.size();i++)
         if(s[i]>''){
             for(int j=i;j<s.size();j++)
                 s[j] = '';
             break;
         }
     x =;
     for(int i=;i<s.size();i++){
         x = x|((s[s.size()--i]-'')<<i);
     }
     return x;
 }

 int cal(int x,int k){
     int tot =,ans =;
     for(int i=;i>;i--){
         if(x&(<<i)){
             tot++;
             if(tot>k) break;
             x = x^(<<i);
         }
         if((<<(i-))<=x){
             ans += f[i-][k-tot];
         }
     }
     if(tot + x==k) ans++;
     return ans;
 }

 int main()
 {
     init();
     int x,y;
     int k,b;
     cin>>x>>y>>k>>b;
     x= change(x,b);
     y = change(y,b);
     int resx = cal(x-,k);
     int resy = cal(y,k);
     cout<<resy-resx<<endl;
     return ;
 }