/Algorithm-Exercises

Leetcode questions, exercise with solutions, classified algorithms.

Primary LanguagePython

Explanation inside the code.

Key functions added in the end of each question.

For question details, please go to Leetcode

  1. Breadth First Search

    • Easy 101 Symmetric Tree -- [re = list(reversed(li))]
    • Easy 107 Binary Tree Level Order Traversal II --[results[::-1]]
    • Easy 559 Maximum Depth of N-ary Tree
    • Medium 993 Cousins in Binary Tree
    • Medium 515 Find Largest Value in Each Tree Row --[float('-inf')]

  2. Depth First Search

    Iteration VS recursive.

    • Pre-order traversal
    • In-order traversal
    • Post-order traversal
    • Medium 200 Number of Islands

  3. Hashing

    The use of collections.Counter() and dictionary.

    • Easy 884 Uncommon Words from Two Sentences -- [collections.Counter()]
    • Easy 387 First Unique Character in a String -- [collections.Counter()]--[float('inf')]--[index = string.find('c')]
    • Easy 1512. Number of Good Pairs [math.comb(n,k)]
    • Medium 347 Top K Frequent Elements -- [counts = sorted(dic.values())]
    • Easy 1 Two Sum -- [for i,item in enumerate(nums)]
    • Medium 3 Longest Substring Without Repeating Characters
    • Medium 146. LRU Cache -- [collections.OrderedDict()]--[dict.popitem(last=False)]

  4. Sliding window

    When to use sliding window? Question like:

    • "finding the substring that meet certain criterion."

    Right pointer loop through list, while substr does not meet criterion, do something that impact the criterion move left pointer

    • Medium 438 Find All Anagrams in a String
    • Medium 209. Minimum Size Subarray Sum
    • Medium 904. Fruit Into Baskets

  5. Linked List

    • Medium 2 Add Two Numbers -- [carry = carry//10]
    • Medium 19 Remove Nth Node From End of List
    • Easy 21 Merge Two Sorted Lists

  6. Tree

    • Medium 105 Construct Binary Tree from Preorder and Inorder Traversal -- recursive

  7. Two Pointers

    When to use two pointers? Question like:

    • "handle the list/string IN PLACE, I want to do something when elements meet certain criterion"
    • Medium 763 Partition Labels
    • Easy 27. Remove Element
    • Easy 283. Move Zeroes
    • Easy 844. Backspace String Compare
    • Easy 977. Squares of a Sorted Array

  8. Array-binary search

    • Easy 937. Reorder Data in Log Files -- [list.sort(reverse=False, key=(key1,key2))]
    • Easy 704. Binary Search -- [Binary Search]
    • Easy 69. Sqrt(x) -- [Binary Search]
    • Easy 367. Valid Perfect Square -- [Binary Search]