Do all the Leetcode problems from the "Google Problems" section. Don't worry if you're not applying to Google. And don't be a cry baby. Just do them all and you'll be in a better shape.
Be able to implement any of these from scratch
Try implementing these.
Heapsort - Sort it in-place to get O(1) space
Selections - Kth Smallest Elements (Sort, QuickSelect, Mediums of Mediums) - Implement all three ways
Tree Traversals - BFS, DFS (in-order, pre-order, post-order): Implement Recursive and Iterative
External Sort - No implementation
Detect cycle in an undirected graph
Detect cycle in a directed graph
Count connected components in graph
Find strongly connected components in graph