Tuesday, February 22, 2011

WAP to Implement Merge Sort Algorithm

public class MergeSortOptimized{

public static int SIZE = 1000000;

public static void main(String args[]){
int[] a = new int[SIZE];
for(int i=0;ia[i] = (int)(Math.random()*SIZE);
}
long start = System.currentTimeMillis();
MergeSortOptimized mNew = new MergeSortOptimized();
mNew.sort(a);
long end = System.currentTimeMillis();
System.out.println("Time taken to sort a million elements : "+(end-start)+" milliseconds");
}

public int[] sort(int[] input){
int[] temp = new int[input.length];
mergeSort(input, temp, 0, input.length-1);
return input;
}

public void mergeSort(int[] fromArray, int[] toArray, int left, int right){
if(leftint center = (left+right)/2;
mergeSort(fromArray, toArray, left, center);
mergeSort(fromArray, toArray, center+1, right);
merge(fromArray, toArray, left, center+1, right);
}
}

public void merge(int[] fromArray, int[] toArray, int leftPos, int rightPos, int rightEnd){
int leftEnd = rightPos - 1;
int tempPos = leftPos;

int numElements = rightEnd - leftPos + 1;

while(leftPos<=leftEnd && rightPos<=rightEnd){
if(fromArray[leftPos]toArray[tempPos++] = fromArray[leftPos++];
}else{
toArray[tempPos++] = fromArray[rightPos++];
}
}

while(leftPos<=leftEnd){
toArray[tempPos++] = fromArray[leftPos++];
}
while(rightPos<=rightEnd){
toArray[tempPos++] = fromArray[rightPos++];
}

for(int i=0;ifromArray[rightEnd] = toArray[rightEnd];
}

}

}
//Time taken to sort a million elements : 247 milliseconds


Some Quick Sort Implementation http://www.algolist.net/Algorithms/Sorting/Quicksort
http://scanftree.com/Data_Structure/Quick-Sort 

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