This table of contents will serve as a tracker of what I have completed so far.
Excellence is an art won by training and habituation. We do not act rightly because we have virtue or excellence, but we rather have those because we have acted rightly. We are what we repeatedly do. Excellence, then, is not an act but a habit. - Aristotle
A list of all the questions I've practiced so far may be seen here. The time complexity, languages employed, and basic idea behind the solution are all included.
| Question Name | Difficulty | Time Complexity | Topic | Language | Main Idea |
|---|---|---|---|---|---|
| Two Sum | Easy | O(n) |
Hash Tables | Python, JavaScript | Use a hash table to store and compare values of an array. This leads to faster time complexity than using a double for loop. |
| Power of Two | Easy | O(log n) |
Binary Operations | Python, JavaScript | Binary representation and operations can be used to locate a pattern in powers of two. |
| Merge Intervals | Medium | O(n log n) |
Arrays | Python | Store the values of a 2d array in a single array and compare values, then store values needed in a new array. |
| Populating Next Right Pointers Each Node | Medium | O(n) |
Nodes | Python | Breadth first search using a queue to store values, assign node values to each other using curr.left or curr.right. |
| Fib Memoization | Easy | O(n) |
Binary Search Tree & HashMap | Python | We use a hash map to store and recall values that we already computed. |
| Plus One | Easy | O(n) |
Arrays | Python | Use a string to convert an array on ints into an integer. |
| Binary Tree Cameras | Hard | O(n) |
DFS | Python | Use dfs bottom up approach (post order traversal) to determine if the node should be a camera or monitored. |
| Search Suggested Item | Medium | O(n) |
Dict | Python | Use dictionaries to compare lists and create new array with comparison outcome |
| Short Encoding of Words | Medium | (On) |
DFS | Python | Create a trie structure with insert then use dfs to take length of words with no children and then add them up |
| Furthest Building | Medium | O(nlogn) |
Priority queue & Greedy | Python | use greedy method implementing a priority queue to trace where you can use bricks and ladders |
| Kth Largest Element | Medium | (Ologn) |
Arrays | Python | sort array and then return k element of the array |
| Course Schedule 3 | Hard | O(nlogn) |
Heap | Python | Keep courses that work inside heap, if the current course is better fit then we swap them from heap |
| Construct Target Array With Multiple Sums | Hard | O(n) |
Heap | Python | Use a heap to store new sums, if the num is less than the target then return false |
| Maximum Points You Can Obtain | Medium | O(n) |
Array | Python | Use a sliding two pointer system to calculate what distribution of left and right would be the best |
| Minimum Deletions to Make Char Freq Unique | Medium | O(n) |
Array, Greedy | Python | count and sort frequencies of each char, then delete those that are the same frequency |
| Queue Reconstruction by Height | Medium | O(nlog) |
Array, Greedy | Python | Use the .sort function and lamda key to sort by decreasing height & within the same height group sort by increasing order of k, then insert into answer array |
| Find Pivot Index | Easy | O(n) |
Array, Prefix Sum | Python | Use total sum of array and prefix sum to calculate the left and right side sums of the array pivot index |
| Min Moves 2 | Medium | O(n) |
Array, Absolute Value | Python | Use the midpoint of a sorted array as the targer, then use the absolute value of i - target to find the amout of moves needed |
| Maximum Sort | Easy | O(nlogn) |
Array, Greedy | Python | Use sorted funtion with key lambda to sort from highest boxes to lowest boxes then use gready algo to find the max boxes |
| Max Area | Medium | O(nlogn) |
Array, Greedy | Python | Sort horizontal and vertical cuts then iterate through them and keep track of max diff |
| Interleaving String | Medium | O(n * m) |
DP | Python | Build dp matrix to calculate solution |
| Matchsticks to Square | Medium | O(n) |
DP, DFS | Python | Build a dictionary for DP and find all possible ways to arrange matchsticks |
| Level Order Traversal | Easy | O(n) |
Recursion | Python | Recurseive pre order traversal call dfs on right and left nodes |
| Construct Binary Tree | Medium | O(n) |
Recursion, DFS | Python | Recursivly create left and right subtrees by passing params |
| Invert Binary Tree | Easy | O(n) |
Binary Tree, Recursion, DFS | Python | Swap left and right nodes, then use dfs to repeat the process |
| Max Area of Islands | Medium | O(mn) |
DFS, Recursion, Matrix | Python | Use dfs on every node horizontal or veritical, set node to 0 if already visited so we do not recount. Increment count each time there is a another 1 attached to the node. |
| Out of Bounds Paths | Medium | O(n) |
DP, Recursion | Python | Use recursion to calculate the max out of bounds moves |
| Climbing Stairs | Easy | O(n) |
DP, Recursion | Python | Set up a helper function (DP HELPER) to calculate climbing stairs n-2 + n-1. Set up base case exits for 0,1. |
| Reverse Linked List 2 | Medium | O(n) |
LinkedList, HashMap | Python | Set up a dummy linked list, use a hashmap to store values from l - r. Use map to resort values. |