[51 nod]1009 数字1的数量

 1 #include<bits/stdc++.h>
 2 #define LL long long 
 4 using namespace std;
 5 LL f(LL n) {
 6         LL count = 0;
 7         LL i = 1;
 8         LL current = 0, after = 0, before = 0;
 9         //int t=0;
10         while ((n / i) != 0) {
11             current = (n / i) % 10;
12             before = n / (i * 10);
13             after = n - (n / i) * i;
14             if (current > 1)
15                 count = count + (before + 1) * i;
16             else if (current == 0)
17                 count = count + before * i;
18             else if (current == 1)
19                 count = count + before * i + after + 1;
20             i = i * 10;
21             //printf("t:%d before:%d current:%d after:%d count:%d\n",++t,before,current,after,count);
22         }
23         return count;
24 }
25 int main(){
26     LL n;
27     cin>>n;
28     cout<<f(n)<<endl;
29 }