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Kaitian Xie
Kaitian Xie

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LeetCode in Ruby: 771 Jewels and Stones

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This approach is based on Ruby’s String#count method. It takes the string j as the set of characters to count in the string s. This is the fastest and the simplest solution.

Time complexity: O(j.length+ s.length)

Extra memory: O(1)


def num_jewels_in_stones(j, s)
  stones = 0
  s.each_char do |char|
    stones[char] += 1

  sum = 0
  j.each_char do |char|
    sum += stones[char]

  return sum

First, we iterate through the string s and create a hash called stones that uses the characters in s as keys and their occurrence as values. Then we go through each character of j and sum up their occurrences.

Time complexity: O(j.length+ s.length)

Extra memory: O(s.length)

Top comments (1)

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Andrew Healey

Awesome solution. This is my favourite problem on LeetCode. It’s a simple introduction to hashmaps and why they’re amazing 👏