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栈与队列

发表于 更新于 分类于 Valine：
栈与队列

栈与队列相互实现

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//栈实现队列
class MyQueue {
public:
    MyQueue() : s_in() , s_out() 
    {}
    
    void push(int x) {
        s_in.push(x);        
    }
    
    int pop() {
        if(s_out.empty()) 
            while(!s_in.empty())
            {
                s_out.push(s_in.top());
                s_in.pop();
            }
        int tmp=s_out.top();
        s_out.pop();
        return tmp;
    }
    
    int peek() {
        int tmp=this->pop();
        s_out.push(tmp);
        return tmp;
    }
    
    bool empty() {
        return s_in.empty() && s_out.empty();
    }
private:
    stack<int> s_in;
    stack<int> s_out;
};
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//队列实现栈
class MyStack {
public:
    MyStack() : q() 
    {}
    
    void push(int x) {
        q.push(x);
    }
    
    int pop() {
        int t=q.size()-1;
        while(t--)
        {
            q.push(q.front());
            q.pop();
        }
        int tmp=q.front();
        q.pop();
        return tmp;
    }
    
    int top() {
        return q.back();
    }
    
    bool empty() {
        return q.empty();
    }
private:
    queue<int> q;
};

单调队列

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//最大值总是在队首
class MonotonicQueue
{
public:
    MonotonicQueue();
    void push(int val);
    void pop(int val);
    int getmax(){return q.front();}
private:
    deque<int> q;
};
MonotonicQueue::MonotonicQueue() : q()
{}
void MonotonicQueue::push(int val)
{
    while(!q.empty() && q.back()<val) q.pop_back();
    q.push_back(val);
}
void MonotonicQueue::pop(int val)
{
    if(!q.empty() && val==q.front()) q.pop_front();
}

滑动窗口最大值

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class Solution {
public:
    vector<int> maxSlidingWindow(vector<int>& nums, int k) {
        vector<int> ans;
        MonotonicQueue sq;
        for(int i=0;i<k;++i) sq.push(nums[i]);
        ans.push_back(sq.getmax());
        for(vector<int>::size_type j=k;j<nums.size();++j){
            sq.pop(nums[j-k]);
            sq.push(nums[j]);
            ans.push_back(sq.getmax());
        }
        return ans;
    }
};