﻿ C exercises: Find the first missing positive integer from a given unsorted integer array - w3resource # C Exercises: Find the first missing positive integer from a given unsorted integer array

## C Programming Practice: Exercise-28 with Solution

Write a C programming to find the first missing positive integer from a given unsorted integer array.

C Code:

``````//https://github.com/begeekmyfriend/leetcode/blob/master/041_first_missing_positive/missing_positive.c
#include <stdio.h>
#include <stdlib.h>
static inline void swap_val(int *x, int *y)
{
int tmp = *x;
*x = *y;
*y = tmp;
}

static int first_Missing_Positive_num(int* nums, int nums_size)
{
if (nums_size < 1) {
return 1;
}

int i = 0;
while (i < nums_size) {
if (nums[i] != i + 1 && nums[i] > 0 && nums[i] <= nums_size && nums[i] != nums[nums[i] - 1]) {
swap_val(nums + i, nums + nums[i] - 1);
} else {
i++;
}
}

for (i = 0; i < nums_size; i++) {
if (nums[i] != i + 1) break;
}
return i + 1;
}

int main()
{
int i, count = 4;
int nums = {3,4,-1,1};

printf("%d\n", first_Missing_Positive_num(nums, count));
return 0;
}
``````

Sample Output:

```2
```

Flowchart: ## C Programming Code Editor:

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## C Programming: Tips of the Day

The tilde operator in C:

The ~ operator is bitwise NOT, it inverts the bits in a binary number:

```NOT 011100
= 100011
```

Ref : https://bit.ly/3DR1N24