First Missing Positive

Question

Find the smallest positive integer which is not present in a given array of integers.

Example 1

Input: [3,4,-1,1]
Output: 2

Solution

▭

all//First Missing Positive.py

def firstMissingPositive(nums):
  if not nums:
    return 1

  # change negative values to 1
  for i in range(len(nums)):
    if nums[i] <= 0:
      nums[i] = 1

  for i in range(len(nums)):
    number = abs(nums[i])
    if number < len(nums):
      nums[number] = -abs(nums[number])

  for i in range(1, len(nums)):
    if nums[i] > 0:
      return i

  return len(nums)

▯

all//First Missing Positive.py

def firstMissingPositive(nums):
  if not nums:
    return 1

  # change negative values to 1
  for i in range(len(nums)):
    if nums[i] <= 0:
      nums[i] = 1

  for i in range(len(nums)):
    number = abs(nums[i])
    if number < len(nums):
      nums[number] = -abs(nums[number])

  for i in range(1, len(nums)):
    if nums[i] > 0:
      return i

  return len(nums)