http://oj.acm.zstu.edu.cn/JudgeOnline/problem.php?cid=4034&pid=7

C++版本一

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,q,ans,l,r,s;
int a;
char str;
int f(int x){
    int ans=x;
    while(x){
        ans-=x%10;
        x/=10;
    }
    return ans;
}
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    while(~scanf("%d%d%d",&l,&r,&s)){
        ans=0;
        t=l;
        while(l<=r){
            int mid=(l+r)>>1;
            if(f(mid)<s){
                ans=mid;
                l=mid+1;
            }else{
                r=mid-1;
            }

        }
        if(ans!=0)
            cout << ans-t+1 << endl;
        else
            cout<<0<<endl;
    }
    //cout << "Hello world!" << endl;
    return 0;
}

C++版本二

题解：因为S小于1e9，所以最大符合条件应该略大于（s+9*9），而[L,S]范围内应该全部满足，所以从[S+1,S+200]遍历再加上S-L+1。

#include<stdio.h>
#include<math.h>
#include<algorithm>
#include<string.h>
using namespace std;
 
int f(int n){
    int ans=0;
    while(n){
        ans=ans+n%10;
        n/=10;
    }
    return ans;
}
 
int main(){
    int l,r,s,swa;
    while(~scanf("%d%d%d",&l,&r,&s)){
        if(l>r){
            swa=l;
            l=r;
            r=swa;
        }
        if(s>=r){
            printf("%d\n",r-l+1);
            continue;
        }
        int ans=0,maxn=s+200,i;
        if(s>l){
            ans=s-l+1;
            l=s+1;
        }
        if(r<maxn)maxn=r;
        for(i=l;i<=maxn;i++)
            if(i-f(i)<s)ans++;
        printf("%d\n",ans);
    }
    return 0;
}