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100+ Coding Interview Problems with Detailed Solutions

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Motivation

Keeping some tracking of most frequently appeared coding interview problems that provided me valuable and productive to spend time on. For each one, some brainstorming about process on how to approach and solve it, adding well-documented solutions with test cases, time and space complexity analysis. May this help you get good algorithms and data structures so that you can prepare better for your next coding interviews.

These resources that I am looking at are:

• Interview Cake
• LeetCode
• Cracking the Coding Interviews
• Grokking the Coding Interview: Patterns for Coding Questions
• Elements of Programming Interviews

Table of Contents

• Interview Cake
  • Array and string manipulation
    • Merge meeting times
    • Reverse string in place
    • Reverse words
    • Merge sorted arrays
    • Single riffle shuffle
  • Hashing and hash tables
    • In-flight entertainment
    • Permutation palindrome
    • Word cloud data
    • Top scores
    • Find duplicate files
  • Greedy algorithms
    • Apple stocks
    • Highest product of three
    • Product of all other numbers
    • In-place shuffle
  • Sorting, searching, and logarithms
    • Find rotation point
    • Find repeat
  • Trees and graphs
    • Balanced binary tree
    • Binary search tree checker
    • 2nd largest item in a binary search tree
    • Graph coloring
    • MeshMessage
  • Dynamic programming and recursion
    • Recursive string permutations
    • Compute nth Fibonacci number
    • Making change
    • The cake thief
  • Queues and stacks
    • Largest stack
    • A queue with two stacks
    • Parenthesis matching
    • Bracket validator
  • Linked lists
    • Delete node
    • Linked list has a cycle
    • Reverse a linked list
    • Kth to last node
  • General programming
    • Rectangular love
    • Temperature tracker
  • Bit manipulation
    • The stolen breakfast drone
  • Combinatorics, probability, and other math
    • Which appears twice
    • Find in ordered set
    • Simulate 5-sided die
    • Simulate 7-sided die
    • Two egg problem
  • TODO: System Design
• Practical Algorithms and Data Structures
• LeetCode
  • Array/String
    • Two sum I
    • Two sum II
    • Valid palindrome
    • Implement strstr()
    • Reverse words in string
    • String to integer
    • Valid number
    • Longest substring without repeating characters
      • TODO: read more about sliding windows problem here
    • Missing ranges
    • One edit distance
    • Read n characters given Read4
  • Math
    • Reverse integer
    • Plus one
    • Palindrome number
  • Linked list
    • Merge sorted linked list
    • Add two numbers
    • Swap nodes in pairs
    • Merge k sorted linked list
    • Copy list with random pointer
  • Binary tree
    • Validate binary search tree
    • Maximum depth of binary tree
    • Minimum depth of binary tree
    • Balanced binary tree
    • Convert sorted array to balanced binary search tree
    • Convert sorted linked list to balanced binary search tree
    • Binary tree maximum path sum
    • Binary tree upside down
  • Bit manipulation
    • Single number I
    • Single number II
  • Misc
    • Spiral matrix
    • Integer to roman
    • Roman to integer
    • Clone graph
  • Stack
    • Min stack
    • Evaluate reverse polish notation
    • Valid parenthesis
  • Dynamic programming
    • Climbing stairs
    • Unique paths
    • Maximum sum subarray
    • Maximum product max array
    • Coins in a line
  • Binary search
    • Search insert position
    • Find minimum in sorted rotated array
• Cracking the Coding Interviews
  • Bit manipulation
    • Bit operation
    • Bit insertion
• Elements of Programming Interviews
• Grokking the Coding Interview: Patterns for Coding Questions
  • Sliding Window
    • Average of any contiguous subarray of size k
    • Maximum sum of any contiguous subarray of size k
    • Smallest subarray with a given sum
    • Longest substring with k distinct characters
    • Fruits into baskets
    • Longest substring without repeating characters
    • Longest substring after k replacements
    • Longest substring after ones replacements
    • Permutation in string
    • String anagrams
    • Smallest window containing substring
    • Words concatenation
  • Two pointers
    • Pair with target sum
    • Remove duplicates
    • Squaring a sorted array
    • Triplet sum to zero
    • Triplet sum close to target
    • Triplet with smaller sum
    • Subarray with product less than a target
    • Dutch national flag problem
  • Fast and slow pointers
    • Linked list cycle
    • Start of a linked list cycle
    • Happy number
    • Middle of a linked list
    • Palindrome linked list
    • Reorder a linked list
  • Merge intervals
    • Merge intervals
    • Insert interval
    • Intervals intersection
    • Conflicting appointment
  • Cyclic sort
    • Cyclic sort
    • Missing number
    • Missing numbers
    • Find duplicate
    • Find duplicates
    • Find corrupt pair
  • In-place reversal of a linked list
    • Reverse a linked list
  • Tree breath first search
    • Binary tree level order traversal
    • Reverse level order traversal
    • Zigzag traversal
    • Level averages
    • Minimum depth
    • Maximum depth
    • Level order successor
  • Tree depth first search
    • Binary tree path sum
    • Sum of path numbers
• Other
  • Data structures
    • Linked List
    • Queue
    • Stack
    • Tree
      • Balanced binary tree
      • Binary tree traversals
    • Graph
    • Trie
    • Heap
    • Priority Queue
    • Bloom filter
    • LRU cache
  • Sorting
    • Bubble sort
    • Selection sort
    • Insertion sort
    • Merge Sort
    • Quicksort
    • Heapsort
    • Counting Sort
    • Radix Sort

Developing

Count the number of questions:

make count

Clean up, lint source files, run tests and be ready for a push:

make ready

Test only:

make test

Test and report:

make cover

Test verbose:

make test-verbose

Lint:

make lint

Clean up:

make clean

For more information:

make help

References

• Sorting algorithm cheat sheet
• LeetCode patterns
• LeetCode's 50 common interview questions
• Practical Algorithms and Data Structures