Number of Digit One

Title: Number of Digit One Source:

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.


  1. Beware of overflow.

Java solution

Number of Digit One
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