求从1到参数n中的各个数字中,各个位上1出现的次数和

/**
	 * 求从1到参数n中的各个数字中,1出现的次数和
	 * 
	 * @param n
	 * @return
	 */
	public static int countOne(int n) {
		int factor = 1;
		int cur;
		int low;
		int high;
		int cnt = 0;
		while ((n / factor) != 0) {
			low = n - (n / factor) * factor;// 低位数字
			cur = (n / factor) % 10;// 当前位数字
			high = n / (factor * 10);// 高位数字

			switch (cur) {
			case 0:
				cnt += high * factor;//由高位决定
				break;
			case 1:
				cnt += high * factor + low + 1;
				break;
			default:
				cnt += (high + 1) * factor;
			}
			factor *= 10;
		}
		return cnt;
	}