Week7 (Apr 29)

347. Top K Frequent Elements

Question

Given an integer array

$nums$ and an integer

$k$, return the

$k$ most frequent elements. You may return the answer in any order.

Constraints:

• $1<=nums.length<=105$
• $-104<=nums[i]<=104$
• $k$ is in the range [1, the number of unique elements in the array].
• It is guaranteed that the answer is unique.

Follow up:
Your algorithm's time complexity must be better than

$O(nlogn)$, where n is the array's size.

Hand in homework before Saturday.

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210. Course Schedule II

Question

There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [

$a_i$,

$b_i$] indicates that you must take course

$b_i$ first if you want to take course

$a_i$.

• For example, the pair [0, 1], indicates that to take course 0 you have to first take course 1.

Return the ordering of courses you should take to finish all courses. If there are many valid answers, return any of them. If it is impossible to finish all courses, return an empty array.

Hand in homework before Saturday.

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