find 2 sum

Time:O(n);Space:O(n)
hash table
find 3 sum

Time:O(n^2); Space:O(1)
find longest consecutive sequence

Time:O(n), Space:O(n);
hash table
find median of two sorted array

Time:O(log(m+n)),Space:O(1);
implement a function to find kth elements in two sorted arrays first
simple
can be followed up by k duplicates are allowed problem
binary search
binary search