[LeetCode 233] Number of Digit One

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.

Hint:

• 1. Beware of overflow.

Diffculty
Hard

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Analysis