PAT-Advanced Math

Abstract：数论相关，虽然有些可以不用数学方法解

1049 Counting Ones (30分)

解法一

参考LeetCode 233 官方题解

#include<iostream>
#include<algorithm>

int countDigitOne(int n)
{
    int countr = 0;
    for (long long i = 1; i <= n; i *= 10) {
        long long divider = i * 10;
        countr += (n / divider) * i + std::min(std::max(n % divider - i + 1, 0LL), i);
    }
    return countr;
}

int main() {
	int num, sum = 0;
	std::cin  >> num;
	std::cout << countDigitOne(num);
}