Is there a way to coalesce repeated numbers in a list using streams in Java 8?

Question

e.g.#1 [1, 1, 1, 2, 22, 35, 35, 120, 320] ==>> [3, 2, 22, 70, 120, 320]

note how repeated consecutive 1\'s and 35\'s are coalesced to 3 and 70

Answer 1

Here is an approach using a stack.

public static List coalesce(List list) {
    Stack stack = new Stack<>();
    stack.addAll(list);
    List sums = new ArrayList<>();
    int sum = 0;
    while (!stack.isEmpty()) {
       int val = stack.pop();
       sum += val;
       if (!stack.isEmpty() && stack.peek() != val) {
          sums.add(0,sum);
          sum = 0;
       }
    }
    sums.add(0,sum);
    return sums;
}