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[0]);
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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Next: Find a subarray with given sum from the given array.
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