今日头条笔试 10.8 第一题

#include<iostream>
#include<math.h>
#include<algorithm>
#include<string.h>
#include<string>
#include<stdio.h>
#include<fstream>
using namespace std;
const long long MOD=1000000007;
 
int inv(int a)
{
    return a==1?1:(long long)(MOD-MOD/a)*inv(MOD%a)%MOD;
}
long long  C(long long n,long long  m)
{
    if(m<0)return 0;
    if(n<m)return 0;
    if(m>n-m)m=n-m;
    long long up=1,down=1;
    for(long long  i=0;i<m;i++)
    {
        up=up*(n-i)%MOD;
        down=down*(i+1)%MOD;
    }
    return up*inv(down)%MOD;
}
int main(){
    int a,b,k;     
    cin>>a>>b>>k;     
    long long ans =0;
    for(int i=0;i<=k;i++){         
    int sum = i * a + (k-i) *b;         
    int flag = 0;         
    while(sum){             
	    if(sum%10 == a || sum %10 == b){                 
		    sum/=10;                 
		    continue;             
	    }             
	    flag=1;             
	    break;         
	    }         
	    if(flag==0){             
	    	ans = (ans+C(k,i))%MOD;         
	    }
    }     
    cout<<ans<<endl;
    return 0;
}