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Remove Element: two pointers approach

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This commit is contained in:
Vitor Oliveira 2021-03-15 21:41:43 -07:00
parent 780c324417
commit ad35c2398c
1 changed files with 27 additions and 2 deletions
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29
data_structures/arrays/remove_elements.rb
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@ -1,7 +1,7 @@
# Arrays - Remove Elements # Arrays - Remove Elements
# #
# Given an array nums and a value val, remove all instances of that value in-place and return the new length. # Given an array nums and a value val, remove all instances of that value in-place and return the new length.
# Do not allocate extra space for another array, # Do not allocate extra space for another array,
# you must do this by modifying the input array in-place with O(1) extra memory. # you must do this by modifying the input array in-place with O(1) extra memory.
# The order of elements can be changed. It doesn't matter what you leave beyond the new length. # The order of elements can be changed. It doesn't matter what you leave beyond the new length.
# #
@ -37,7 +37,7 @@ def remove_elements(nums, val)
result_length = nums.length result_length = nums.length
shift_length = 0 shift_length = 0
nums.each_with_index do |num, i| nums.each_with_index do |num, i|
if num == val if num == val
nums.delete_at(i) nums.delete_at(i)
nums.unshift('removed') nums.unshift('removed')
result_length -=1 result_length -=1
@ -52,3 +52,28 @@ puts remove_elements([3,2,2,3], 3)
# => 2 # => 2
puts remove_elements([0,1,2,2,3,0,4,2], 2) puts remove_elements([0,1,2,2,3,0,4,2], 2)
# => 5 # => 5
#
# Approach 3: Two-pointer
#
def remove_element(nums, val)
pointer1 = 0
pointer2 = nums.length
while pointer1 < pointer2
if nums[pointer1] == val
nums[pointer1] = nums[pointer2 - 1]
pointer2 -= 1
else
pointer1 += 1
end
end
pointer1
end
puts remove_elements([3,2,2,3], 3)
# => 2
puts remove_elements([0,1,2,2,3,0,4,2], 2)
# => 5