UNB/ CS/ David Bremner/ teaching/ java/ MergeSort3.java
```public class MergeSort3
{
/**
Merges two adjacent subranges of an array
@param a the array with entries to be merged
@param from the index of the first element of the
first range
@param mid the index of the last element of the
first range
@param to the index of the last element of the
second range
*/
public static void merge(int[] a,
int from, int mid, int to)
{  int n = to - from + 1;         // size of the range to be merged

int[] b = new int[n]; // merge both halves into a temporary array b

int i1 = from;         // next element to consider in the first range
int i2 = mid + 1;      // next element to consider in the second range
int j = 0;             // next open position in b

// as long as neither i1 nor i2 past the end, move the smaller into b
while (i1 <= mid && i2 <= to)
{  if (a[i1] < a[i2])
{  b[j] = a[i1];
i1++;
}
else
{  b[j] = a[i2];
i2++;
}
j++;
}

// note that only one of the two while loops
// below is executed

// copy any remaining entries of the first half
while (i1 <= mid)
{  b[j] = a[i1];
i1++;
j++;
}

// copy any remaining entries of the second half
while (i2 <= to) {
b[j] = a[i2];
i2++;
j++;
}

// copy back from the temporary array
for (j = 0; j < n; j++)
a[from + j] = b[j];
}
//
/**
Sorts a range of an array, using the merge sort
algorithm.
@param a the array to sort
@param from the first index of the range to sort
@param to the last index of the range to sort
*/
public static void mergeSort(int[] a, int from,
int to){
if (from == to) return;
int mid = (from + to) / 2;

mergeSort(a, from, mid);
mergeSort(a, mid + 1, to);

merge(a, from, mid, to);
}
/**
Sorts an array, using the merge sort algorithm.
@param a the array to sort
*/
public static void sort(int[] a)
{  mergeSort(a, 0, a.length - 1);
}

public static void main(String[] args){
int [] data= ArrayUtil.randomIntArray(10,1000);

ArrayUtil.print(data);

sort(data);

ArrayUtil.print(data);

}

}
//

```