LeetCode [220] Contains Duplicate III

Ref
[1] https://leetcode.com/problems/contains-duplicate-iii/
OJ
[2] https://leetcode.com/discuss/38206/ac-o-n-solution-in-java-using-buckets-with-explanation
bucket sort
[3] https://leetcode.com/discuss/45120/c-using-set-less-10-lines-with-simple-explanation
set