return k-th to last
problem
Implement an algorithm to find the kth to last element of a singly linked list
how to solve
We use two pointers slow-pointer and fast-pointer. Firstly we proceed the fast-pointer in k step. Secondly, we move them at the same pace and slow pointer will hit the end of the linked list after k length . This algorithm takes O(n) time and O(1) space.
code
Atcoder Grand Contest : B Splatter Painting
problem
how to solve
The limitation of d is very small and it is key point to solve this problem. Consider that dp[v][i] which means “paint dp[v][i] among the range d distance from vertex v”. The time complexity is O(d(n+m) + q)
code
Evaluate Division
problem
Equations are given in the format A / B = k, where A and B are variables represented as strings, and k is a real number (floating point number). Given some queries, return the answers. If the answer does not exist, return -1.0.
Example: Given a / b = 2.0, b / c = 3.0. queries are: a / c = ?, b / a = ?, a / e = ?, a / a = ?, x / x = ? . return [6.0, 0.5, -1.0, 1.0, -1.0 ].
The input is: vector<pair<string, string>> equations, vector
how to solve
I can solve this problem by using Warshall–Floyd algorithm. So I have to create the adjacent matrix. To do so, I create the hash table which the key is string and the value is integer for storing the index of string. This time complexity is O(n3).
code
Trie tree
What is Trie tree?
Trie tree is a data structure of handling string. - Looking up data in a trie is faster in the worst case O(m)(m is the length of a search string). - There are no collisions of different keys in a trie. - There is no need to provide a hash function or to change hash functions as more keys are added to a trie.
Implementation
First Common Ancestor
problem
Design an algorithm and write code to find the first common ancestor of two nodes in a binary tree. Avoid storing additional nodes in a data structure. NOTE: This is not necessarily a binary search tree.
how to solve
Starting from root node and check whether p or q is existed in subtree. If left subtree includes one node and right subtree includes the other node, we can decided that the current node is lowest common ancestor.
code
Word Break (LeetCode)
problem
Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, determine if s can be segmented into a space-separated sequence of one or more dictionary words. You may assume the dictionary does not contain duplicate words.
For example, given s = “leetcode”, dict = [“leet”, “code”].
Return true because “leetcode” can be segmented as “leet code”.
how to solve
https://leetcode.com/articles/word-break/
