PAT A급 1049.Counting Ones (30)

1924 단어 PAT A급
The task is simple: given any positive integer N, you are supposed to count the total number of ones in the decimal form of the integers from 1 to N. For example, given N being 12, there are five ones in 1, 10, 11, and 12. Input Specification: Each input file contains one test case which gives the positive N (<= 230 ). Output Specification: For each test case, print the number of 1’s in one line. Sample Input: 12 Sample Output: 5
// 。  
#include 
using namespace std;

int main(){
    int N;
    cin>>N;

    int count=0;
    int x=1;
    while(N/x>0){
        int current=(N/x)%10;
        int left=N/(10*x);
        int right=N%x;
        if(current<1) count+=left*x;
        else if(current==1) count+=(left*x+right+1);
        else count+=(left+1)*x;
        x*=10;
    }
    cout<return 0;
}

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