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  • 1049 Counting Ones (30)

    The task is simple: given any positive integer N, you are supposed to count the total number of 1's in the decimal form of the integers from 1 to N. For example, given N being 12, there are five 1's in 1, 10, 11, and 12.

    Input Specification:

    Each input file contains one test case which gives the positive N (<=2^30^).

    Output Specification:

    For each test case, print the number of 1's in one line.

    Sample Input:

    12

    Sample Output:

    5
    #include<cstdio>
    int main(){
        int n;
        scanf("%d",&n);
        int a = 1,left,now,right,ans = 0;
        while(n/a){
            left = n / (a*10);
            right = n % a;
            now = n / a % 10;
            if(now == 0) ans += left*a;
            else if(now == 1) ans += left*a + right + 1;
            else ans += (left+1)*a;
            a *= 10; 
        }
        printf("%d",ans);
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/wanghao-boke/p/9520043.html
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