Tag: leetcode

Link: https://leetcode.com/problems/flip-equivalent-binary-trees/  Thought If 2 nodes are equivalent, either their left and right side match, or they are flipped match. So using a recursion(why recursion? It is a Tree!), and try to match each node pairs from root1 and root2. For each recursion level, I will first compare if current node pair have the same value. […]

link: https://leetcode.com/problems/reveal-cards-in-increasing-order/ Thought So the rule is if you pop anything from front, then you shall move next head to tail. Reversely, if we want to build the original sequence, we could assume if you want to insert anything in head, you should pop your tail, and push the tail to head Code Runtime Time: O(n)Space: […]

link: https://leetcode.com/problems/largest-time-for-given-digits/ Thought Its easy to think use DFS to solve it: it has limit data(4 digits), and DFS will enumerates all possible combinations Code Runtime Time: O(n!)Space: O(n!)

Link: Most Stones Removed with Same Row or Column Thought When I saw the question, I realized its a Union Find question – For any union, I can keep only one stone form it. Then it convert to a count how many unique union finds exist question.  So, only need to count all unique union find, […]

Link:  validate stack sequences Thought Its pretty straight forward, just stimulate a stack and push/pop as the sequence shows.  Code Runtime Time: O(n) Space: O(n)

Link: Bag of Tokens Thought For this question, I find we could do 2 things: spend any cost form the tokens, and get 1 point. Or, spend 1 point, get any power from the tokens. So it turns to be pretty clear that I will firstly sort all tokens by value, and trying to get […]

Link Minimum Increment to Make Array Unique Thought Firstly, I try to enumerate all existing number, and I got TLE :(. Then I realized I could sort the origin array and maintain a upper boundary, for any number, if it smaller than upper boundary, means I can only move it to upper boundary + 1 […]

link: Minimum Area Rectangle Thought I plan to use sweep line to solve. Firstly I put a dictionary with x-val as key, all y-val with coordinate x-val as value. Then, once I check x1, x2, if they has intersection, means there could be a rectangle. So I could enumerate all possible rectangles and record the […]

link: Range Sum of BST Thought When first saw this question, I think using tree traverse could solve it and it did works. Code Runtime Time O(n) Space O(n)

link Distinct Subsequences II Thought The very first thought here is use DFS to find all distinct subsequences. However it will time out. So my next idea is using dynamic programming to solve it. I’ll define a DP array, where DP[i + 1] stands for how many distinct subsequences if I use 0,1,…i characters to […]