Given an integer n, count the total number of digit 1 appearing in all non-negative integers less than or equal to n. For example: Given n = 13, Return 6, because digit 1 occurred in the following numbers: 1, 10, 11, 12, 13.
public class Solution { public int countDigitOne(int n) { int multiply = 1; int sum = 0; int input = n; int stub = 0; while (n > 0) { if (n % 10 > 0) { stub = n / 10 + 1; sum += (n / 10 + 1) * multiply; } else { stub = n / 10; sum += (n / 10) * multiply; } if (n % 10 == 1 && n / 10 > 0) { sum -= (stub * multiply - input % (multiply * 10) - 1) % multiply; } else if (n % 10 == 1 && n / 10 == 0) { sum -= (stub * multiply - input % (multiply) - 1) % multiply; } multiply = multiply * 10; n = n / 10; } return sum; } }
原文：http://www.cnblogs.com/fgynew/p/5141495.html