ural1057 Amount of degrees 位数统计

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

int f[33][33];
void init(){
    f[0][0] =1;
    for(int i=1;i<=31;i++){
        f[i][0] = f[i-1][0];
        for(int j=0;j<=i;j++)
            f[i][j] = f[i-1][j]+f[i-1][j-1];
    }
}

int change(int x,int b){
    string s;
    while(x){
        s = (char)(x%b+'0')+s;
        x = x/b;
    }
    for(int i=0;i<s.size();i++)
        if(s[i]>'1'){
            for(int j=i;j<s.size();j++)
                s[j] = '1';
            break;
        }
    x =0;
    for(int i=0;i<s.size();i++){
        x = x|((s[s.size()-1-i]-'0')<<i);
    }
    return x;
}

int cal(int x,int k){
    int tot =0,ans =0;
    for(int i=31;i>0;i--){
        if(x&(1<<i)){
            tot++;
            if(tot>k) break;
            x = x^(1<<i);
        }
        if((1<<(i-1))<=x){
            ans += f[i-1][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-1,k);
    int resy = cal(y,k);
    cout<<resy-resx<<endl;
    return 0;
}