RecursiveMergeSort.java

public class RecursiveMergeSort {
	static void mergeSort(int arr[], int n) 
    { 
          
        // For current size of subarrays to 
        // be merged curr_size varies from  
        // 1 to n/2 
        int curr_size;  
                      
        // For picking starting index of  
        // left subarray to be merged 
        int left_start; 
                          
          
        // Merge subarrays in bottom up  
        // manner. First merge subarrays  
        // of size 1 to create sorted  
        // subarrays of size 2, then merge 
        // subarrays of size 2 to create  
        // sorted subarrays of size 4, and 
        // so on. 
        for (curr_size = 1; curr_size <= n-1;  
                      curr_size = 2*curr_size) 
        { 
              
            // Pick starting point of different 
            // subarrays of current size 
            for (left_start = 0; left_start < n-1; 
                        left_start += 2*curr_size) 
            { 
            	int mid = Math.min(left_start + curr_size - 1, n-1); 
                
                int right_end = Math.min(left_start  
                             + 2*curr_size - 1, n-1); 
          
                // Merge Subarrays arr[left_start...mid] 
                // & arr[mid+1...right_end] 
                merge(arr, left_start, mid, right_end); 
            } 
        } 
    } 
      
    /* Function to merge the two haves arr[l..m] and 
    arr[m+1..r] of array arr[] */
    static void merge(int arr[], int l, int m, int r) 
    { 
        int i, j, k; 
        int n1 = m - l + 1; 
        int n2 = r - m; 
      
        /* create temp arrays */
        int L[] = new int[n1]; 
        int R[] = new int[n2]; 
      
        /* Copy data to temp arrays L[] 
        and R[] */
        for (i = 0; i < n1; i++) 
            L[i] = arr[l + i]; 
        for (j = 0; j < n2; j++) 
        	R[j] = arr[m + 1+ j]; 
        
        /* Merge the temp arrays back into 
        arr[l..r]*/
        i = 0; 
        j = 0; 
        k = l; 
        while (i < n1 && j < n2) 
        { 
            if (L[i] <= R[j]) 
            { 
                arr[k] = L[i]; 
                i++; 
            } 
            else
            { 
                arr[k] = R[j]; 
                j++; 
            } 
            k++; 
        } 
      
        /* Copy the remaining elements of  
        L[], if there are any */
        while (i < n1) 
        { 
            arr[k] = L[i]; 
            i++; 
            k++; 
        } 
        while (j < n2) 
        { 
            arr[k] = R[j]; 
            j++; 
            k++; 
        } 
    } 
    static void printArray(int arr[]) 
    { 
        int n = arr.length; 
        for (int i=0; i<n; ++i) 
            System.out.print(arr[i] + " "); 
        System.out.println(); 
    }
    
    public static void main(String[]args) {
		
		int[]arr1= {34,19,2,9,1,55,0,33,4,99,54,23,12};
		mergeSort(arr1,12);
		printArray(arr1);
		
	}
}