347. Top K Frequent Elements

Given a non-empty array of integers, return the k most frequent elements. For example, Given [1,1,1,2,2,3] and k = 2, return [1,2]. Note:
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160. Intersection of Two Linked Lists

Write a program to find the node at which the intersection of two singly linked lists begins.   For example, the following two linked lists:
A:          a1 → a2
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