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Insertion Sort in C++
What is Insertion Sort in C++?
Rearranging data in a logical order is known as sorting i.e. arranging of data in ascending or descending order. In this article, we will learn about insertion sort in C++.
Insertion sorting is done in the same way as we sort our cards in while we play games of cards
Time Complexity | O(n2) |
Best Case | Ω(n) |
Worst Case | O(n2) |
Aux. Space Complexity | O(1) |
Best case when | Array is already sorted |
Worst case when | Array is reverse sorted |
Insertion Sort in C++
If there are n element and it requires (n-1) pass to sort them then, at each pass we insert current element in the appropriate position so that the element are in order. Some characteristics of insertion sort in C++.
- A sub-list is maintained which is always in sorted order.
- It is better then Selection Sort and Bubble Sort algorithms.
- It is efficient for smaller data sets but inefficient for larger data sets.
- Its space complexity is less.
- It does not change the relative order of elements which are equal.
Execution of insertion sort in C++
- It’s almost similar to how we play cards.
- At any given time, one part of the array will be sorted and one part will be unsorted.
- We will pick the leftmost item from the unsorted part
- Insert this item at the correct position in the sorted array
You can check the implementation of the same below
Algorithm for insertion sort in C++
- INSERTION-SORT(A)
- for i = 1 to n
- key ← A [i]
- j ← i – 1
- while j > = 0 and A[j] > key
- A[j+1] ← A[j]
- j ← j – 1
- End while
- A[j+1] ← key
- End for
Program for insertion sort in C++
// C++ Program for Insertion Sort // Time Complexity : O(N^2) // Space Compelexity : O(1) // Best Case : When already Sorted, Worst Case : When reverse Sorted #include<iostream> using namespace std; //Function to print array. void display(int arr[], int size) { int i; for (i = 0; i < size; i++) cout << arr[i] << "\t"; cout << "\n"; } //Main function to run the program. int main() { int array[] = {5, 3, 1, 9, 8, 2, 4,7}; int size = sizeof(array)/sizeof(array[0]); cout << "Before Insertion sort: \n"; display(array, size); int i, key, j; for (i = 1; i < size; i++) { key = array[i]; j = i - 1; /* Here the elements in b/w arrary[i-1 & 0] which are greater than key are moved ahead by 1 position each*/ while (j >= 0 && array[j] > key) { array[j + 1] = array[j]; j = j - 1; // moving backwards } // placing key item now array[j + 1] = key; } cout << "After Insertion sort: \n"; display(array, size); return 0; }
Output
Before Insertion sort: 5 3 1 9 8 2 4 7 After Insertion sort: 1 2 3 4 5 7 8 9
Pros and Cons of Insertion Sort Algorithm
Pros
- Anyone can write it is moderately easy to understand
- Only O(1) space requirements
- For a smaller number of items in an array it’s quicker than merge sort
Cons
- Not so good average time complexity of O(n2)
- If there are large elements then it gives bad performance because of O(n^2) time complexity
- Shifting items because of insertion can be costly
Other information
- Best Case: If already sorted data set
- Worst Case: Sorted data set but in the opposite order
Sorting
Sorting algorithms are easy to learn but are really important for college semester exams and companies offering package between 3 – 6 LPA would ask direct searching questions in online test/ interviews.
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