LeetCode 233.Number of Digit One

Problem Description

Given an integer n, count the total number of digit 1 appearing in all non-negative integers less than or equal to n.

Example 1:

Input: n = 13
Output: 6

Example 2:

Input: n = 0
Output: 0

Constraints:

0 <= n <= 109

Link

https://leetcode.com/problems/number-of-digit-one/