How to find the max value of an Arraylist and two of its Index position using Java

问题

How can I find the maximum value from an Arraylist with its index positions?

ArrayList ar = new ArrayList();
ar.add(2); // position 0
ar.add(4); // position 1
ar.add(12); // position 2
ar.add(10); // position 3
ar.add(12); // position 4

String obj = Collections.max(ar);
int index = ar.indexOf(obj);

System.out.println("obj max value is " + obj + " and index position is " + index);

The above program just returns the output as the first max object with value 12 and index position 2.

But my actual output should be index positions 2 and 4 (because max value 12 is present in two index position).

回答1:

Untested:

public static int maxIndex(List<Integer> list) {
  Integer i=0, maxIndex=-1, max=null;
  for (Integer x : list) {
    if ((x!=null) && ((max==null) || (x>max))) {
      max = x;
      maxIndex = i;
    }
    i++;
  }
  return maxIndex
}
// ...
maxIndex(Arrays.asList(1, 2, 3, 2, 1)); // => 2
maxIndex(Arrays.asList(null, null)); // => -1
maxIndex(new ArrayList<Integer>()); // => -1

回答2:

You can use Collections to find the max value of a list, and then use the property indexOf to find its position in your list.

List<Integer> myList = new ArrayList<Integer>();
myList.add(3); // adding some values
myList.add(5);
myList.add(7);
myList.add(3);
myList.add(1);

Integer maxVal = Collections.max(myList); // should return 7
Integer maxIdx = myList.indexOf(maxVal); // should return 2 (position of the value 7)

回答3:

Just iterate once through list, have another list to push index of maximum number

回答4:

Since Java 8 this could be done by:

int index = IntStream.range(0, ar.size()).boxed()
        .max(Comparator.comparing(ar::get)).orElse(-1);

回答5:

public static void main(String[] args){

    List<Integer> ar=new ArrayList<Integer>();
    ar.add(2); `adding the values in the list`
    ar.add(5);
    ar.add(6);
    ar.add(4);
    ar.add(6);
    ar.add(5);
    ar.add(6);

    int max=Collections.max(ar);

    while(ar.contains(max))
    {
        int i=ar.indexOf(max); 
        System.out.println("the index of 6:"+ar.indexOf(max));
        ar.set(i, -1);
        System.out.println(ar);
    }

}

来源：https://stackoverflow.com/questions/10437623/how-to-find-the-max-value-of-an-arraylist-and-two-of-its-index-position-using-ja

标签

java

arraylist