Exercise_4.java

// Time Complexity : O(n log n)
// Space Complexity : O(n) 
// Did this code successfully run on Leetcode : Yes
// Any problem you faced while coding this :
// No major issues. The tricky part was correctly dividing the array,
// creating temporary subarrays, and ensuring all remaining elements
// from each subarray were copied back into the main array.



// I used the classic Merge Sort algorithm, which divides the array
// into two halves recursively until each subarray has one element.
// Then the merge() function is used to combine the two sorted halves
// by comparing elements and placing them in the correct order.
// The merge step uses temporary arrays to store left and right halves.
// Finally, the sorted values are copied back into the original array.
class MergeSort 
{ 
    // Merges two subarrays of arr[]. 
    // First subarray is arr[l..m] 
    // Second subarray is arr[m+1..r] 
    void merge(int arr[], int l, int m, int r) 
    {  
	int n1 = m - l + 1;
 	int n2 = r - m;
	int L[] = new int[n1];
	int R[] = new int[n2];
	for (int i = 0; i < n1; ++i)
	L[i] =arr[l + i];

	for (int j = 0; j < n2; ++j)
	R[j] = arr[m + 1 +j];
int i = 0, j = 0;
int k = l;
while (i < n1 && j < n2){
	if (L[i] <= R[j])
	{
		arr[k] = L[i];
		i++;
	}else{
		arr[k] = R[j];
		j++;
	}
	k++;
}
while (i < n1){
	arr[k] = L[i];
	i++;
	k++;
}while(j < n2){
	arr[k] = R[j];
	j++;
	k++;
}//Your code here  
    } 
  
    // Main function that sorts arr[l..r] using 
    // merge() 
    void sort(int arr[], int l, int r) 
    { 
	if(l < r){
		int m =(l + r) / 2;
		sort(arr, l, m);
		sort(arr, m + 1, r);
		merge(arr, l, m, r);
	}//Write your code here
        //Call mergeSort from here 
    } 
  
    /* A utility function to print array of size n */
    static void printArray(int arr[]) 
    { 
        int n = arr.length; 
        for (int i=0; i<n; ++i) 
            System.out.print(arr[i] + " "); 
        System.out.println(); 
    } 
  
    // Driver method 
    public static void main(String args[]) 
    { 
        int arr[] = {12, 11, 13, 5, 6, 7}; 
  
        System.out.println("Given Array"); 
        printArray(arr); 
  
        MergeSort ob = new MergeSort(); 
        ob.sort(arr, 0, arr.length-1); 
  
        System.out.println("\nSorted array"); 
        printArray(arr); 
    } 
}