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Review: Hashmap Problems

Posted on January 31, 2018July 26, 2020 by braindenny

Review Hashmap code problems



Top Questions

Name Example
Use a local hashmap, instead of a global one LeetCode: Increasing Subsequences
One hashmap vs two hashmap LeetCode: Before and After Puzzle
Hashmap may make code more complicated LeetCode: Find K-th Smallest Pair Distance
Mapping data range of getRand algorithm LeetCode: Implement Rand10() Using Rand7()
Contains Duplicate II Leetcode: Contains Duplicate II
Rolling hash  
  • Use a tuple as key

Group Shifted Strings

## Blog link: https://code.dennyzhang.com/group-shifted-strings
class Solution:
    def groupStrings(self, strings):
        """
        :type strings: List[str]
        :rtype: List[List[str]]
        """
        import collections
        m = collections.defaultdict(list)
        for s in strings:
            # ba -> (0, 25)
            # az -> (0, 25)
            tup = tuple([(ord(ch)-ord(s[0]))%26 for ch in s])
            m[tup].append(s)
        return [m[key] for key in m]

  • CheatSheet: Leetcode For Code Interview
  • CheatSheet: Common Code Problems & Follow-ups

See all hashmap problems: #hashmap

  • Review: Hashmap Problems
  • LintCode: Word Frequency Count
  • LintCode: Valid Array
  • LintCode: Same Number
  • LintCode: Longest AB Substring
  • LintCode: Function Runtime
  • LintCode: Fermat Point Of Graphs
  • LeetCode: X of a Kind in a Deck of Cards
  • LeetCode: Vowel Spellchecker
  • LeetCode: Verifying an Alien Dictionary
  • LeetCode: Unique Word Abbreviation
  • LeetCode: Unique Number of Occurrences
  • LeetCode: Unique Morse Code Words
  • LeetCode: Unique Email Addresses
  • LeetCode: Uncommon Words from Two Sentences
  • LeetCode: Two Sum IV – Input is a BST
  • LeetCode: Triples with Bitwise AND Equal To Zero
  • LeetCode: Sum of Distances in Tree
  • LeetCode: Subdomain Visit Count
  • LeetCode: Subarray Sum Equals K
  • LeetCode: Split Array with Equal Sum
  • LeetCode: Smallest Integer Divisible by K
  • LeetCode: Simplified Fractions
  • LeetCode: Shortest Word Distance II
  • LeetCode: Shortest Completing Word
  • LeetCode: Sentence Similarity
  • LeetCode: Reduce Array Size to The Half
  • LeetCode: People Whose List of Favorite Companies Is Not a Subset of Another List
  • LeetCode: Pairs of Songs With Total Durations Divisible by 60
  • LeetCode: Number of Distinct Islands
  • LeetCode: Number of Boomerangs
  • LeetCode: Number of Atoms
  • LeetCode: Minimum Number of Frogs Croaking
  • LeetCode: Minimum Area Rectangle II
  • LeetCode: Maximum Number of Balloons
  • LeetCode: Make Two Arrays Equal by Reversing Sub-arrays
  • LeetCode: Longest String Chain
  • LeetCode: Longest Repeating Substring
  • LeetCode: Longest Harmonious Subsequence
  • LeetCode: Longest Duplicate Substring
  • LeetCode: Line Reflection
  • LeetCode: Largest Component Size by Common Factor
  • LeetCode: Kill Process
  • LeetCode: K-diff Pairs in an Array
  • LeetCode: Jump Game IV
  • LeetCode: Jewels and Stones
  • LeetCode: Intersection of Two Arrays
  • LeetCode: Increasing Subsequences
  • LeetCode: H-Index
  • LeetCode: Group Shifted Strings
  • LeetCode: Group Anagrams
  • LeetCode: Graph Valid Tree
  • LeetCode: Friends Of Appropriate Ages
  • LeetCode: Fraction to Recurring Decimal
  • LeetCode: First Unique Number
  • LeetCode: Find Words That Can Be Formed by Characters
  • LeetCode: Find Smallest Common Element in All Rows
  • LeetCode: Find Duplicate Subtrees
  • LeetCode: Find Duplicate File in System
  • LeetCode: Find and Replace Pattern
  • LeetCode: Fair Candy Swap
  • LeetCode: Distinct Echo Substrings
  • LeetCode: Diagonal Traverse II
  • LeetCode: Destination City
  • LeetCode: Design Underground System
  • LeetCode: Design Excel Sum Formula
  • LeetCode: Counting Elements
  • LeetCode: Count Vowels Permutation
  • LeetCode: Count Number of Nice Subarrays
  • LeetCode: Contains Duplicate II
  • LeetCode: Contains Duplicate
  • LeetCode: Confusing Number
  • LeetCode: Check If N and Its Double Exist
  • LeetCode: Check If a String Contains All Binary Codes of Size K
  • LeetCode: Brick Wall
  • LeetCode: Array of Doubled Pairs
  • LeetCode: 4Sum II

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