https://loj.ac/problem/10163
#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>
#include <map>
#include <string>
#include <iostream>
#include <cmath>
using namespace std;
#define Del(a,b) memset(a,b,sizeof(a))
typedef long long LL;
const double esp = 1e-10;
const int N = 50;
int f[N][N];
void isit()
{
f[0][0] = 1;
for(int i=1;i<33;i++){
f[i][0] = f[i-1][0];
for(int j=1;j<=i;j++)
f[i][j] = f[i-1][j] + f[i-1][j-1];
}
}
int solve(int x,int k,int c)
{
vector<int> v;
while(x)
{
v.push_back(x%c);
x/=c;
}
int cnt = 0,ans = 0;
for(int i=v.size()-1;i>=0;i--)
{
if(v[i]==1)
{
ans+=f[i][k-cnt];
cnt++;
if(cnt==k)
break;
}
else if(v[i]>1)
{
ans += f[i+1][k-cnt];
break;
}
}
if(cnt==k)
ans++;
return ans;
}
int main()
{
isit();
int x,y,k,c;
while(~scanf("%d%d%d%d",&x,&y,&k,&c))
{
printf("%d\n",solve(y,k,c)-solve(x-1,k,c));
}
return 0;
}