剑指offer：整数中1出现的次数（从1到n整数中1出现的次数）

 1 public int NumberOf1Between1AndN_Solution(int n) {
 2     int count = 0;
 3     while (n > 0) {
 4         String nStr = String.valueOf(n);
 5         for (int i = 0; i < nStr.length(); i++) {
 6             if (nStr.charAt(i) == ‘1‘)
 7                 count++;
 8         }
 9         n--;
10     }
11     return count;
12 }

 1 public int NumberOf1Between1AndN_Solution(int n) {
 2     int low = 0, cur = 0, high = 0;
 3     int count = 0;
 4     int factor = 1;
 5     while (factor <= n) {
 6         high = n / (factor * 10);
 7         low = n % factor;
 8 //            cur = (n - high * (factor * 10) - low) / factor;
 9         cur = (n / factor) % 10;
10         if (cur == 0)
11             count += high * factor;
12         else if (cur == 1)
13             count += high * factor + low + 1;
14         else
15             count += (high + 1) * factor;
16         factor *= 10;
17     }
18     return count;
19 }