# First Missing Integer Interviewbit Solution

**Problem: **__First Missing Integer__

**Problem Description:**

Given an unsorted integer array, find the first missing positive integer.

**Example:**

```
Given [1,2,0] return 3,
[3,4,-1,1] return 2,
[-8, -7, -6] returns 1
```

Your algorithm should run in O(n) time and use constant space.

**Solution: **

**Method 1:**

```
Time Complexity: O(N)
Space Complexity: O(N)
```

**Method 2:**

```
Time Complexity: O(NlogN)
Space Complexity: O(1)
```

### Method 3:

```
Time Complexity: O(N)
Space Complexity: O(1)
```

It looks in the code given above , first approach missed space constraints and second approach missed time constraint. ( As per InterviewBit problem statement)