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Language/Type: Java ArrayList Collections mystery
Author: Roy McElmurry

Consider the following method:

public static void mystery4(ArrayList<Integer> list) { 
    for (int i = list.size() - 2; i > 0; i--) { 
        int a = list.get(i); 
        int b = list.get(i + 1); 
        list.set(i, a + b); 

Write the output produced by the method when passed each of the following ArrayLists:

[72, 20]
[1, 2, 3, 4, 5, 6]
[10, 20, 30, 40]

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