Last Updated: 9 Jun, 2023
Reverse an Array
Easy
Asked in companies
Given an array 'arr' of size 'n'.
Return an array with all the elements placed in reverse order.
Note:
You don’t need to print anything. Just implement the given function.
Example:
Input: n = 6, arr = [5, 7, 8, 1, 6, 3]
Output: [3, 6, 1, 8, 7, 5]
Explanation: After reversing the array, it looks like this [3, 6, 1, 8, 7, 5].
Input Format:
The first line contains an integer n, the size of the array
The second line contains n integers, the array.
Output format:
Return the reversed array.
Approaches
Approach:
- Create a new array, say, ‘arr1’.
- Iterate from index ‘0’ to ‘n-1’ and arr1[i] = arr[n-1-i]
Algorithm:
- Create a new array arr1 of size n
- For ‘i’ from 0 to n-1
- arr1[i] =arr[n-1-i];
- Return arr1;
Approach:
- Initialize two pointers, start pointing to the first element of the array, and end pointing to the last element of the array.
- Swap the elements at the start and end indices, increment the start pointer, and decrement the end pointer.
- Repeat the swap until the start pointer crosses the end pointer.
- The array will be reversed in-place.
Algorithm:
- int i = 0 , j = n-1;
- while(i<=j)
- swap(arr[i] , arr[j]);
- i++;
- j–;
- Return arr;
Approach:
- Implement a recursive function to reverse the array.
- Base case: If the start index is greater than or equal to the end index, return.
- Swap the elements at the start and end indices.
- Recursively call the reverse function with start+1 and end-1.
- The array will be reversed in-place.
Algorithm:
- Void reverse(int arr[], int i, int j)
- if(i > j) return;
- swap(arr[i], arr[j]);
- return reverse(arr , i+1 , j-1);
Approach:
In C++:
- Include the algorithm header file to access the std::reverse function.
- Use the std::reverse function with the range specified by the bidirectional iterators 'first' and 'last' to reverse the elements in the array.
- Syntax: std::reverse(array_name.begin(), array_name.end())
- Note: The range includes the first element but excludes the last element.
In Java:
- Import the reverse method from the Collections class in java.util package.
- Convert the array into a list object using the asList method, as Java collections require wrapper classes instead of primitive data types.
- Use the Collections.reverse method to reverse the list object.
- Syntax: Collections.reverse(Arrays.asList(array_name))
- Note: If the array contains integer values, use the Integer wrapper class instead of the int data type.
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