【剑指Offer】（栈和队列）滑动窗口的最大值（双端队列）

傷城~ 2022-03-15 07:38 125阅读 0赞

**题目链接**：[https://www.nowcoder.com/practice/1624bc35a45c42c0bc17d17fa0cba788?tpId=13&tqId=11217&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking][https_www.nowcoder.com_practice_1624bc35a45c42c0bc17d17fa0cba788_tpId_13_tqId_11217_tPage_1_rp_1_ru_ta_coding-interviews_qru_ta_coding-interviews_question-ranking]

#### 题目描述 ####

给定一个数组和滑动窗口的大小，找出所有滑动窗口里数值的最大值。例如，如果输入数组\{2,3,4,2,6,2,5,1\}及滑动窗口的大小3，那么一共存在6个滑动窗口，他们的最大值分别为\{4,4,6,6,6,5\}； 针对数组\{2,3,4,2,6,2,5,1\}的滑动窗口有以下6个： \{\[2,3,4\],2,6,2,5,1\}， \{2,\[3,4,2\],6,2,5,1\}， \{2,3,\[4,2,6\],2,5,1\}， \{2,3,4,\[2,6,2\],5,1\}， \{2,3,4,2,\[6,2,5\],1\}， \{2,3,4,2,6,\[2,5,1\]\}。

#### 解决方法 ####

class Solution { 
    public:
        vector<int> maxInWindows(const vector<int>& num, unsigned int size)
        { 
            
            vector<int> res;
            if(num.size()<=0 || size<=0 || num.size()<size) return res;
            
            //使用双端队列deque，deque只保存可能是滑动窗口最大值的数值所对应的下标
            deque<int> slip;
            //初始化第一个窗口
            for(int i=0;i<size;i++){ 
                while(!slip.empty() && num[i]>=num[slip.back()])
                    slip.pop_back();
                slip.push_back(i);
            }
            res.push_back(num[slip.front()]); 
            //开始滑动
            for(int i=size;i<num.size();i++){ 
                while(!slip.empty() && num[i]>=num[slip.back()])
                    slip.pop_back();
                if(!slip.empty() && slip.front()==i-size) //当前最大的元素（队头）被滑走了，则弹出它
                    slip.pop_front();
                slip.push_back(i);
                res.push_back(num[slip.front()]);                        
            }
            return res;
        }
    };

[https_www.nowcoder.com_practice_1624bc35a45c42c0bc17d17fa0cba788_tpId_13_tqId_11217_tPage_1_rp_1_ru_ta_coding-interviews_qru_ta_coding-interviews_question-ranking]: https://www.nowcoder.com/practice/1624bc35a45c42c0bc17d17fa0cba788?tpId=13&tqId=11217&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking