1-n中1出现的次数

//直接算，蛮力法

public int NumberOf1Between1AndN_Solution(int n) {        int ans = 0;        for (int i = 1; i < n + 1; i++) {            ans += singleNum(i);        }        return ans;    }    private int singleNum(int i) {        int num = 0;        while (i != 0) {            boolean flag = ((i % 10) == 1);            if (flag) num++;            i/=10;        }        return num;    }