题解 | #整数中1出现的次数）#

不用数位dp，纯计算的最简代码

public class Solution {
    public int NumberOf1Between1AndN_Solution(int n) {
        int ret = 0;
        for (long m = 1; m <= n; m *= 10) {
            long a = n / m, b = n % m;
            ret += (a + 8) / 10 * m + (a % 10 == 1 ? b + 1: 0);
        }
        return ret;
    }
}