﻿ C : Smallest positive number missing in an unsorted array

# C Exercises: Find the smallest positive number missing from an unsorted array

## C Array: Exercise-46 with Solution

Write a program in C to find the smallest positive number missing from an unsorted array.

Visual Presentation: Sample Solution:

C Code:

``````#include <stdio.h>
#include <stdlib.h>

// Function to swap two integers
void swap(int *a, int *b)
{
int tmp;
tmp = *a;
*a = *b;
*b = tmp;
}

// Function to separate positive and negative numbers
int separateNvePsvNumbers(int arr1[], int arr_size)
{
int j = 0, i;
for (i = 0; i < arr_size; i++)
{
if (arr1[i] <= 0)
{
swap(&arr1[i], &arr1[j]);
j++;
}
}
return j; // Return the position where positive numbers start
}

// Function to find the smallest positive missing number
int getMissPosNumber(int arr1[], int arr_size)
{
int i;
// Modify array elements to mark presence of numbers
for (i = 0; i < arr_size; i++)
{
if (abs(arr1[i]) - 1 < arr_size && arr1[abs(arr1[i]) - 1] > 0)
arr1[abs(arr1[i]) - 1] = -arr1[abs(arr1[i]) - 1];
}
// Return the smallest positive missing number
for (i = 0; i < arr_size; i++)
if (arr1[i] > 0)
return i + 1; // Indexes start from 0, so add 1 to get the number
return arr_size + 1; // If no positive numbers found, return arr_size + 1
}

// Function to get the smallest positive missing number in the array
int GetSmalPosMisNum(int arr1[], int arr_size)
{
int shift = separateNvePsvNumbers(arr1, arr_size);
return getMissPosNumber(arr1 + shift, arr_size - shift);
}

int main()
{
int arr1[] = {3, 1, 4, 10, -5, 15, 2, -10, -20};
int arr_size = sizeof(arr1) / sizeof(arr1);
int i;

// Print the original array
printf("The given array is :  ");
for (i = 0; i < arr_size; i++)
{
printf("%d  ", arr1[i]);
}
printf("\n");

// Get the smallest positive missing number
int miss_num = GetSmalPosMisNum(arr1, arr_size);
printf("The smallest positive number missed is:  %d ", miss_num);
getchar();
return 0;
}
```
```

Sample Output:

```The given array is :  3  1  4  10  -5  15  2  -10  -20
The smallest positive number missed is:  5
```

Flowchart: C Programming Code Editor:

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