剑指 Offer 59 - II. 队列的最大值

方法：维护一个单调的双端队列

 

 1 class MaxQueue {
 2 private:
 3     queue<int> A;
 4     deque<int> B;   
 5 public:
 6     MaxQueue() {
 7 
 8     }
 9     
10     int max_value() {
11         if(B.empty())
12             return -1;
13         return B.front();
14     }
15     
16     void push_back(int value) {
17         A.push(value);
18         while(!B.empty() && value > B.back()) {
19             B.pop_back();
20         }
21         B.push_back(value);
22     }
23     
24     int pop_front() {
25         if(A.empty()) {
26             return -1;
27         } else {
28             int tmp = A.front();
29             A.pop();
30             if(tmp == B.front())    
31                 B.pop_front();
32 
33             return tmp;
34         }
35 
36     }
37 };
38 
39 /**
40  * Your MaxQueue object will be instantiated and called as such:
41  * MaxQueue* obj = new MaxQueue();
42  * int param_1 = obj->max_value();
43  * obj->push_back(value);
44  * int param_3 = obj->pop_front();
45  */

 

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