Java数组降序排列并打印其元素编号

Question

What I am trying to do is sort an array in descending order like this

Arrays.sort(array);
Collections.reverse(Arrays.asList(array));

and then print which array element was first and then second and then thrird etc..

INPUT: 10 43 77 23 the descending order of them is: 77 43 23 10 I want it to print: 3 2 4 1

If you have any questions feel free to ask me.

Thanks you in advance!

Answer 1

If I understand correct, you want to print the index of the element in the original array? First you'll need to copy the array, sort the copy and then find the indices in of the sorted elements in the original array. Following code does that.

int[] x = Arrays.copyOf(array, array.length);
Arrays.sort(x);
Collections.reverse(Arrays.asList(x));

List listObject = Arrays.asList(array)

for(int el : x) {
    System.out.print(listObject.indexOf(el)
}

This is assuming your elements in the array are unique. If the elements in your array are of a different type, you should change the type of x and el accordingly.

Answer 2

You could work with a Map with the element as the key, and the index as the value. You'd first have to create this map with a for loop

Map<Integer, Integer> indexLookUp = new HashMap<>();
for(int i = 0; i < array.length; i++) {
    map.put(array[i], i);
}

Then you can sort the array:

Arrays.sort(array);

You don't need the reversing part, as you can just iterate the array backwards. And then print out the index for the element via the map lookup:

for(int i = array.length - 1; i >= 0; i--) {
    System.out.println("Element: " + array[i] + ", previous index: " + map.get(array[i]));
}

Answer 3

Try this:

int array[] = {17, 10, 8, 13, 5, 7, 8, 30};

// Init the element list
List<Element> elements = new ArrayList<Element>();
for (int i = 0; i < array.length; i++) {
    elements.add(new Element(i, array[i]));
}

// Sort and print
Collections.sort(elements);
Collections.reverse(elements); // If you want reverse order
for (Element element : elements) {
    System.out.println(element.value + " " + element.index);
}

Answer 4

You can sort an array of indices instead of the array containing the actual data:

    Integer[] indices = new Integer[array.length];
    for (int i = 0; i < array.length; ++i) {
        indices[i] = i;
    }
    Arrays.sort(indices, (a, b) -> {
        return array[a] < array[b] ? 1 : array[a] > array[b] ? -1 : 0;});