Find the next greater element in an array (in O(n) time)

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class NextGreaterChallenge {

    public static int[] nextGreaterElement(int[] arr) {

        int[] result = new int[arr.length];

        int resultIndex = 0;

        Stack<Integer> stack = new Stack<>(arr.length);
  
        //Iterate over the array from last
        for (int i = arr.length - 1; i >= 0; i--) {

            //Pop all the elements which are smaller than current element 
            if (!stack.isEmpty()) {
                while (!stack.isEmpty() && stack.top() <= arr[i]) {
                    stack.pop();
                }
            }
  
            //if stack becomes empty, then NGE doesn't exit 
            if(stack.isEmpty()){
                result[i] = -1;
            }

            //If stack is not empty, NGE is top of stack 
            else
                result[i]  = stack.top();

            //Push current element into stack
            stack.push(arr[i]);

        }

        return result;
    }
}