Problems
September 8, 2022
Build an array with stack operations
We will create a stack to match with our target and also create a result list. Then we start a loop from 1 to n and append each number to the stack. If the top of the stack does not match our target,...
ReadSeptember 8, 2022
Robot bounded in circle
The idea is, after the first iteration, if the direction is not north facing or the current position is the start position, then it is a cycle, otherwise not. First if condition basically encounters...
ReadSeptember 8, 2022
Minimum consecutive cards to pick up
We will use a set to keep track of cards in the hand. Initially we will assume the current number of cards in the hand in infinity. We will have 2 pointers, we will move our right pointer, check if...
ReadSeptember 8, 2022
Repeated dna sequences
We will use a sliding window which is 10 characters long. For each window, we will add this to a lookup set. If the window is already present in the lookup set, that means we already have it more...
ReadSeptember 8, 2022
Combination sum III
We will run DFS towards our decision tree, for building a decision tree, we have 2 options, either we take the number or we skip the number. We will check when the sum of the numbers we took is equal...
ReadSeptember 7, 2022
Keys and rooms
We will create a set with all the nodes. First we put them in unvisited set. Then we start traversing the graph using BFS and remove nodes from unvisited set after every node visit. Finally when the...
ReadSeptember 7, 2022
Print binary tree
First we will calculate the height of the tree. Our result will be a 2d matrix where the each row will have 2^height-1 element and there will be height rows in total. We...
September 7, 2022
Construct string from binary tree
We will use recursive DFS to traverse the tree and append the result to a string and return it.
Time Complexity: O(n)
Space Complexity: O(n)
September 6, 2022
Implement magic dictionary
We will use the Trie data structure to store all the elements in the dictionary. Building the dictionary is pretty strait forward, we will insert all the words from the dictionary to the trie. As we...
ReadSeptember 6, 2022
H-index II
We will seach for the highest mid where the value of mid is greater that or equal to the numbers of elements on the right from that mid index.
Time Complexity: O(log(n))
Space...