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  1. // C++ program for the above approach
  2. #include <bits/stdc++.h>
  3. using namespace std;
  4.  
  5. // Function for finding the first
  6. // missing positive number
  7. int firstMissingPositive(int arr[], int n)
  8. {
  9.  
  10. 	// Loop to traverse the whole array
  11. 	for (int i = 0; i < n; i++) {
  12.  
  13. 		// Loop to check boundary
  14. 		// condition and for swapping
  15. 		while (arr[i] >= 1 && arr[i] <= n
  16. 			&& arr[i] != arr[arr[i] - 1]) {
  17. 			swap(arr[i], arr[arr[i] - 1]);
  18. 		}
  19. 	}
  20.  
  21. 	// Checking any element which
  22. 	// is not equal to i+1
  23. 	for (int i = 0; i < n; i++) {
  24. 		if (arr[i] != i + 1) {
  25. 			return i + 1;
  26. 		}
  27. 	}
  28.  
  29. 	// Nothing is present return last index
  30. 	return n + 1;
  31. }
  32.  
  33. // Driver code
  34. int main()
  35. {
  36. 	int arr[] = { 2, 3, -7, 6, 8, 1, -10, 15 };
  37. 	int n = sizeof(arr) / sizeof(arr[0]);
  38.  
  39. 	int ans = firstMissingPositive(arr, n);
  40.  
  41. 	cout << ans;
  42.  
  43. 	return 0;
  44. }
  45. // This code is contributed by Harsh kedia
  46.  
Success #stdin #stdout 0.01s 5352KB
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https://ideone.com/AfzzoG
language:
C++ (gcc 8.3)
created:
51 days ago
visibility:
public

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