LCOF劍指offer--面試題59 - II. 隊列的最大值

分析：
雙端隊列輔助
解答：

class MaxQueue {
public:
    queue<int> que;
    deque<int> deque;
    MaxQueue() {

    }
    
    int max_value() {
        if(que.size()==0) return -1;

        return deque.front();

    }
    
    void push_back(int value) {
        que.push(value);

        if(deque.size()==0){
            deque.push_back(value);
        }
        else if(deque.front()<value){
            deque.clear();
            deque.push_back(value);
        }
        else{
            while(deque.back()<value){
                deque.pop_back();
            }
            deque.push_back(value);
        }

    }
    
    int pop_front() {
        if(que.size()==0) return -1;

        int res = que.front();
        que.pop();

        if(deque.front()==res){
            deque.pop_front();
        }

        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();
 */