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Add solution using a hash

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This commit is contained in:
Jessica Kwok 2021-03-11 15:53:01 -08:00
parent e58e707a57
commit a6ae1c25b5
1 changed files with 27 additions and 2 deletions
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29
data_structures/arrays/two_sum.rb
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@ -24,7 +24,7 @@
# @return {Integer[]}
#
# Approach 1: Brute Force
# Approach 1: Brute Force with Addition
#
# Time Complexity: O(N^2), where N is the length of the array
#
@ -51,7 +51,7 @@ print two_sum([3, 3], 6)
# => [0,1]
#
# Approach 2: Define and seek
# Approach 2: Brute Force with Difference
#
# Time Complexity: O(N^2), where N is the length of the array
#
@ -66,6 +66,31 @@ def two_sum(nums, target)
end
end
print two_sum([2, 7, 11, 15], 9)
# => [0,1]
print two_sum([3, 2, 4], 6)
# => [1,2]
print two_sum([3, 3], 6)
# => [0,1]
#
# Approach 3: Using a Hash
#
# Time Complexity: O(N), where N is the length of the array
#
def two_sum(nums, target)
hash = {}
# create a hash to store values and their indices
nums.each_with_index do |num, i|
hash[num] = i
end
# iterate over nums array to find the target (difference between sum target and num)
nums.each_with_index do |num, i|
difference_target = target - num
return [i, hash[difference_target]] if hash[difference_target] && hash[difference_target] != i
end
end
print two_sum([2, 7, 11, 15], 9)
# => [0,1]
print two_sum([3, 2, 4], 6)