# First missing positive

`Input: nums = [1,2,0]Output: 3`
`Input: nums = [3,4,-1,1]Output: 2`
`Input: nums = [7,8,9,11,12]Output: 1`
• `1 <= nums.length <= 5 * 105`
• `-2^31 <= nums[i] <= 2^31 - 1`
`loop from 1 to length of nums+1:      check if the number is present in the nums array      if number  not present in nums :          return number`
`class Solution(object):    def firstMissingPositive(self, nums):        val=set(nums)        for i in range(1,len(nums)+2):                        if i not in val and i>0:                return i`
`class Solution(object):    def firstMissingPositive(self, nums):        i=0        while(i<len(nums)):            if nums[i]<=0 or nums[i]>len(nums):                i+=1            else:                if nums[i]==i+1:                    i+=1                else:                    if nums[nums[i]-1]==nums[i]:                        i+=1                    else:                        temp=nums[nums[i]-1]                            nums[nums[i]-1]=nums[i]                        nums[i]=temp        j=0        while(j<len(nums)):            if(j+1!=nums[j]):                return(j+1)            j+=1        return(len(nums)+1)`

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## Dhanarajappu

Tech-Enthusiast, Coder,Explorer,Geeky,Software Engineer |A piece of code delivers everything that you need. The world is all about codes.