leetcode
link: Range Sum of BST Thought When first saw this question, I think using tree traverse could solve it and it did works. Code # Definition for a binary tree node. # class TreeNode: # def __init__(self, x): # self.val = x # self.left = None # self.right = None class Solution: def rangeSumBST(self,
leetcode
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
leetcode
link: Number of Recent Calls Thought Question ask for numbers of calls in 3000. So sliding windows is my choice here - it will move and drop calls earlier than 3000 - which I don't care, and keep tracing incoming calls. Code class RecentCounter: def __init__(self): self.t = collections.
leetcode
link Knight Dialer Thought Since it ask how many distinct numbers could be generated, DP jumps to my mind immediately. Firstly, the relation is, if knight stop at number 6, it has to come from 1, 7, or 0. So I keep a DP array, DP[j][i] stands for
leetcode
link: Shortest Bridge Thought Since the question ask for shortest, so BFS probabely the best algorithms to solve it. But notice, I will use 2 bfs funciton, one to find the edge of first island, the other one is to reach another island based on first edge. BFS1: input: start
leetcode
Link 931.Minimum Falling Path Sum Thought DFS When first seeing this question, DFS prompt into my mind directly. Take Any node from first level as start, and search down stream. Until reach node in last level. For any path, it will have a value. Find the minimum value and
leetcode
Link: Unique Email Addresses Thought Brutal Force Solution This question is pretty simple (and it actually is an esay one). A naive approache is, split the name and domain. For the name, remove every thing after first '+', and then replace all '.' as empty. For the domain,