问题
I need to write a program in java to find the median of an array of three or more integers without sorting. I need some ideas. thanks
回答1:
You can use a Selection Algorithm. You'll also find relevant information looking for Median of Medians.
回答2:
You can use Quick sort partitioning step with random pivots, without sorting it.
public class TestMedian {
public static void main(String[] args){
int[] a = {1,9,-4,7,6,11,3,2,10};
int median;
median = new Median().findMedian(a,0,a.length-1);
if(a.length%2 != 0)
System.out.print("the median is : "+a[median]);
else
System.out.print("the median is : "+(a[median] + a[median + 1])/2 );
}
public int findMedian(int[] a,int left,int right){
int index = 0;
int mid = (left+right)/2;
index = partition(a,left,right);
while( index != mid){
if(index < mid)
index = partition(a,mid,right);
else index = partition(a,left,mid);
}
return index;
}
public int partition(int[] a,int i,int j ){
int pivot = (i+j)/2;
int temp;
while(i <= j){
while(a[i] < a[pivot])
i++;
while(a[j] > a[pivot])
j--;
if(i <= j){
temp = a[i];
a[i]=a[j];
a[j] = temp;
i++;j--;
}
}
return pivot;
}
}
来源：https://stackoverflow.com/questions/22096554/finding-the-median-in-java-without-sorting