# First Missing Positive LeetCode Solution

Here, We see First Missing Positive LeetCode Solution. This Leetcode problem is done in many programming languages like C++, Java, JavaScript, Python, etc., with different approaches.

# List of all LeetCode Solution

## Problem Statement

Given an unsorted integer array nums, return the smallest missing positive integer.

```Example 1:
Input: nums = [1,2,0]
Output: 3
Explanation: The numbers in the range [1,2] are all in the array.

Example 2:
Input: nums = [3,4,-1,1]
Output: 2
Explanation: 1 is in the array but 2 is missing.```
```Example 3:
Input: nums = [7,8,9,11,12]
Output: 1
Explanation: The smallest positive integer 1 is missing.```

## First Missing Positive Leetcode Solution C++

``````class Solution {
public:
int firstMissingPositive(vector<int>& nums) {
int n=nums.size();
for(int i=0 ; i<n ; i++)
{
while(nums[i]>0 and nums[i]<=n and nums[i]!=nums[nums[i]-1])
swap(nums[i],nums[nums[i]-1]);
}
for(int i=0 ; i<n ; i++) if(nums[i] != i+1) return i+1;
return n+1;
}
};
```Code language: C++ (cpp)```

## First Missing Positive Leetcode Solution Java

``````class Solution {
public int firstMissingPositive(int[] nums) {
int n = nums.length;
boolean[] exists = new boolean[n];
for (int num : nums) {
if (num > 0 && num <= n) exists[num - 1] = true;
}
for (int i = 0; i < exists.length; i++) {
if (!exists[i]) return i + 1;
}
return n + 1;
}
}
```Code language: Java (java)```

## First Missing Positive Leetcode Solution JavaScript

``````var firstMissingPositive = function(nums) {
for (let i = 0; i < nums.length; i++) {
let idx = nums[i]-1;
if (i == idx || nums[i] == nums[idx]) continue;
if (idx >= 0 && idx <= nums.length - 1) {
[nums[i], nums[idx]] = [nums[idx], nums[i]];
i--;
}
}
for (let i = 0; i < nums.length; i++) {
if (i+1 == nums[i]) continue;
else return i+1;
}
return nums.length + 1;
};
```Code language: JavaScript (javascript)```

## First Missing Positive Leetcode Solution Python

``````class Solution(object):
def firstMissingPositive(self, nums):
unique = set(nums)
i = 1
while i in unique:
i += 1
return i
```Code language: Python (python)```
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