1049 Counting Ones (22/30 分)

1049 Counting Ones

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

代码

22分代码

如果to_string 不可用点击如下链接

https://blog.csdn.net/weixin_44635198/article/details/114404887

#include<bits/stdc++.h>

using namespace std;

int main(){
    
    
	size_t n;
	string str;
	
	cin >> n;
	for(size_t i=1; i<=n; i++) {
    
    
		str += to_string(i);
	}
	
	cout << count(str.begin(),str.end(),'1');
    return 0;
}