Solution.java

class MaxQueue {
    private Deque<Integer> p;
    private Deque<Integer> q;

    public MaxQueue() {
        p = new ArrayDeque<>();
        q = new ArrayDeque<>();
    }

    public int max_value() {
        return q.isEmpty() ? -1 : q.peekFirst();
    }

    public void push_back(int value) {
        while (!q.isEmpty() && q.peekLast() < value) {
            q.pollLast();
        }
        p.offerLast(value);
        q.offerLast(value);
    }

    public int pop_front() {
        if (p.isEmpty()) return -1;
        int res = p.pollFirst();
        if (q.peek() == res) q.pollFirst();
        return res;
    }
}

/**
 * Your MaxQueue object will be instantiated and called as such:
 * MaxQueue obj = new MaxQueue();
 * int param_1 = obj.max_value();
 * obj.push_back(value);
 * int param_3 = obj.pop_front();
 */