剑指 Offer 59 - II. 队列的最大值

思路

方法：维护一个单调的双端队列

 

class MaxQueue {
private:
    queue<int> A;
    deque<int> B;   
public:
    MaxQueue() {

    }
    
    int max_value() {
        if(B.empty())
            return -1;
        return B.front();
    }
    
    void push_back(int value) {
        A.push(value);
        while(!B.empty() && value > B.back()) {
            B.pop_back();
        }
        B.push_back(value);
    }
    
    int pop_front() {
        if(A.empty()) {
            return -1;
        } else {
            int tmp = A.front();
            A.pop();
            if(tmp == B.front())    
                B.pop_front();

            return tmp;
        }

    }
};

/**
 * 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();
 */

 

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