【剑指Offer】43. 从 1 到 n 整数中 1 出现的次数

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

public class Solution {
    public int NumberOf1Between1AndN_Solution(int n) {
        int res = 0, m = 1;
        int high = n / 10, cur = n % 10, low = 0;
        
        while(high != 0 || cur != 0) {
            if(cur == 0) 
                res += high * m;
            else if(cur == 1) 
                res += high * m + low + 1;
            else 
                res += (high + 1) * m;
            
            low += cur * m;
            cur = high % 10;
            high /= 10; 
            m *= 10;
        }
        return res;
    }
}