41. First Missing Positive

https://leetcode.com/problems/first-missing-positive/

JavaScript

/**
 * @param {number[]} nums
 * @return {number}
 */
var firstMissingPositive = function(nums) {
  for (let i = 0; i < nums.length; i++) {
    while (nums[i] > 0 && nums[i] <= nums.length && nums[i] !== i + 1 && nums[i] !== nums[nums[i] - 1]) {
      var temp = nums[i]
      nums[i] = nums[nums[i] - 1]
      nums[temp - 1] = temp
    }
  }

  for (let i = 0; i < nums.length; i++) {
    if (nums[i] !== i + 1) {
      return i + 1
    }
  }

  return nums.length + 1
}

Python

class Solution(object):

    def firstMissingPositive(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        for i in range(len(nums)):
            while nums[i] > 0 and nums[i] <= len(nums) and nums[i] != i + 1 and nums[i] != nums[nums[i] - 1]:
                temp = nums[i]
                nums[i] = nums[nums[i] - 1]
                nums[temp - 1] = temp

        for i in range(len(nums)):
            if nums[i] != i + 1:
                return i + 1

        return len(nums) + 1