My code can be viewed in my github: Proverbs Github.
The following difficulty is defined by myself.
integer-to-english-words(medium)
Divide the number into different parts according to the commas of writing a number.
The most difficult part of the problem is various corner cases, such as when should we output Zero.
alien-dictionary(medium)
Most sort algorithms are based on comparison, so we can exploit lexicographical order by comparing two contiguous words. Then we can represent the relationship using graph and use topological sort to check if there is a loop in the graph.
jewels-and-stones(easy)
license-key-formatting(easy)
meeting-rooms-ii(medium)
As usual, sort the intervals by the start time. Use current rooms as possible as we can. When there is no room available, we should add a new room.
So, the problem is how to judge if there is an available room. At first, I tried to use set and binary search. Then, add current interval to the searched room. Sure it is correct. However, we can find the room which ends earliest and add current interval to this room. It is corret because the following intervals start later then current interval and all available rooms for current interval are also available for the following intervals. Thus, we can add current interval to any one of the
available rooms.
next-closest-time(easy)
Numerate all possible time using brute force and then check if the time is correct. A trick is to add a big number to the time of the next day.
palindrome-number(easy)
Convert a number to a string using sprintf.
reverse-string(easy)
unique-email-addresses(easy)
binary-search-tree-iterator(medium)
I always use a iterator to traverse a set or map, however, I never think about the implementation. The simplest idea is to simulate the stack of traversing. Sure it is correct. But when I was exploring the discussions, I found a more elegant method: pop the node from the stack when walking into its right child.
fizz-buzz(easy)
friend-circles(easy)
Use DFS to find number of blocks of connected nodes.
longest-substring-with-at-most-two-distinct-characters(medium)
Use double pointers to maintain a sliding window. First, move the left pointer and then move the right pointer.
max-area-of-island(easy)
Similar to friend-circles. Use DFS to traverse the whole 2D graph.
utf-8-validation(easy)
Be careful.