刷题打卡 －pxu

just did the 538. Convert BST to Greater Tree. Although it marked as easy question, seems still not easy for me. need to work harder!

finished 661. Image Smoother, still need to the see the discussion. so ashamed. the tricky is creating a new array and the [-1, 0, 1] for row and col;

did 535. Encode and Decode TinyURL. again. weird, leetcode didn't store my last submit.

Completed 535. Encode and Decode TinyURL. almost one time AC. Glad I got some progress finally.cheers,

sorry, wrong question above, should be 645. Set Mismatch. just need to make sure the order in the result array, 0 should be the duplicated one and 1 is the missing one.

finished 762. Prime Number of Set Bits in Binary Representation just now, and the triky part is that you need to manually list the primes and do the right shift on the int.  

just noticed that I have 181 points now. time flies

It took me about 4 hours to figure out and learn 146. LRU Cache. To make it work was fine, you can use map and queue, to make the time complexity  to O(1), have to use either map or doubly linked list with dummy head and tail. what a complex question.

completed 173. Binary Search Tree Iterator. I was able to make the space complexity to O(n) but couldn't make it to O(h). Learned what guru put in the discussion and figured it out. cheers:)

208. Implement Trie (Prefix Tree). key point, isEnd and TreeNode[] = new TreeNode[26] within the TreeNode. Feel a bit tired.