Similar as "Majority Element". There are at most 2 such elements, for > floor(n/3), and every non-hit element will decrease count of EACH hit element.
https://leetcode.com/discuss/42769/o-n-time-and-in-o-1-space-c-solution
LeetCode "Majority Element II"
原文：http://www.cnblogs.com/tonix/p/4609153.html