diff --git a/.DS_Store b/.DS_Store new file mode 100644 index 0000000..992daa1 Binary files /dev/null and b/.DS_Store differ diff --git a/docs/.DS_Store b/docs/.DS_Store new file mode 100644 index 0000000..993e58a Binary files /dev/null and b/docs/.DS_Store differ diff --git a/docs/LeetCode/.DS_Store b/docs/LeetCode/.DS_Store new file mode 100644 index 0000000..8015193 Binary files /dev/null and b/docs/LeetCode/.DS_Store differ diff --git a/docs/LeetCode刷题/1 - 100/_category_.json b/docs/LeetCode/1 - 100/_category_.json similarity index 61% rename from docs/LeetCode刷题/1 - 100/_category_.json rename to docs/LeetCode/1 - 100/_category_.json index 063c1af..7d660de 100644 --- a/docs/LeetCode刷题/1 - 100/_category_.json +++ b/docs/LeetCode/1 - 100/_category_.json @@ -1,4 +1,4 @@ { "label": "1 - 100", - "position": 2 + "position": 3 } diff --git a/docs/LeetCode刷题/1 - 100/hello.md b/docs/LeetCode/1 - 100/hello.md similarity index 100% rename from docs/LeetCode刷题/1 - 100/hello.md rename to docs/LeetCode/1 - 100/hello.md diff --git a/docs/LeetCode刷题/100 - 200/_category_.json b/docs/LeetCode/100 - 200/_category_.json similarity index 63% rename from docs/LeetCode刷题/100 - 200/_category_.json rename to docs/LeetCode/100 - 200/_category_.json index 0e3c226..6b996cf 100644 --- a/docs/LeetCode刷题/100 - 200/_category_.json +++ b/docs/LeetCode/100 - 200/_category_.json @@ -1,4 +1,4 @@ { "label": "100 - 200", - "position": 3 + "position": 4 } diff --git a/docs/LeetCode刷题/100 - 200/hello 100.md b/docs/LeetCode/100 - 200/hello 100.md similarity index 100% rename from docs/LeetCode刷题/100 - 200/hello 100.md rename to docs/LeetCode/100 - 200/hello 100.md diff --git a/docs/LeetCode/CodingInterviews/StackAndQueue/.DS_Store b/docs/LeetCode/CodingInterviews/StackAndQueue/.DS_Store new file mode 100644 index 0000000..b626063 Binary files /dev/null and b/docs/LeetCode/CodingInterviews/StackAndQueue/.DS_Store differ diff --git a/docs/LeetCode/CodingInterviews/StackAndQueue/MaxValueOfQueue.md b/docs/LeetCode/CodingInterviews/StackAndQueue/MaxValueOfQueue.md new file mode 100644 index 0000000..ad89551 --- /dev/null +++ b/docs/LeetCode/CodingInterviews/StackAndQueue/MaxValueOfQueue.md @@ -0,0 +1,183 @@ +# 队列\_剑指Offer59题\_队列的最大值问题 + +## 题目描述如下： + +请定义一个队列并实现函数max\_value得到队列里的最大值，要求函数max\_value、push\_back和pop\_front的均摊时间复杂度都是O(1)。若队列为空，pop\_front和max\_value需要返回-1。 + +示例1: + +~~~shell +输入: +["MaxQueue","push_back","push_back","max_value","pop_front","max_value"] +[[],[1],[2],[],[],[]] +输出: [null,null,null,2,1,2] +~~~ + +示例2: + +```shell +输入: +["MaxQueue","pop_front","max_value"] +[[],[],[]] +输出: [null,-1,-1] +``` + +限制： + +- `1 <= push_back,pop_front,max_value的总操作数 <= 10000` +- `1 <= value <= 10^5` + +代码： + +~~~java +class MaxQueue { + + public MaxQueue() { + + } + + public int max_value() { + + } + + public void push_back(int value) { + + } + + public int pop_front() { + + } +} + +/** + * 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(); + */ +~~~ + +## 思考思路 + +题目的描述中提到了3个方法，其中max\_value是求最大值的，**提到最大值，首先想到这里应该是用到了某种排序的手段**。剩下的两个方法分别是push和pop操作，这明显是栈、队列这块的操作。因此不难想象，这道题用到的数据结构包含某种队列，然后涉及到某种排序方法。 + +本着先实现，后优化的原则，最容易想到的解决方案是这样的： + +用一个队列保存所有的数据，这样保证了push和pop操作是正常执行的。然后将这个队列从大到小排列到另一个数据结构中，这样执行max_value方法时输出数组第一项即可。删除队列中数据的时候，用来排序的数据结构中的对应数据也应该删掉。 + +于是乎很容易写出这样的代码： + +~~~java +class MaxQueue { + + private Queue datas; + + // TODO:排序后的数据暂时用队列保存 + private Queue sortedDatas; + + public MaxQueue() { + this.datas = new LinkedList; + this.sortedDatas = new LinkedList; + } + + public int max_value() { + if (sortedDatas.isEmpty()) { + return -1; + } + return sortedDatas.peekFirst(); + } + + public void push_back(int value) { + datas.offer(value); + sortedDatas = addNewDataAndSortDatas(); + } + + public int pop_front() { + if (datas.isEmpty()) { + return -1; + } + int ans = datas.pool(); + deleteDataFromSortedDatas(ans); + return ans; + } + + private Queue addNewDataAndSortDatas() { + // TODO: 将所有数据排序，然后覆盖原先的sortedDatas + } + + private void deleteDataFromSortedDatas(int ans) { + // TODO: 将ans从sortedDatas队列中删除 + } +} +~~~ + +接下来考虑着三个TODO项如何去解决。首先要确定的是用什么数据结构保存sortedDatas。 + +| 数据结构 | 优劣分析 | 结论 | +| -------- | ------------------------------------------------------------ | ---------- | +| 数组 | 队列中元素个数能达到10000，定义10000长度的数组浪费内存，不定义这么长要考虑扩容，浪费性能。 | :no_entry: | +| 链表 | 不可能用这货排序。 | :no_entry: | +| 栈 | 将数据由小到大存入，能直接取到最大值。删除数据时要再用一个栈倒数据。**正常的排序方法难以实现均摊时间复杂度O(1)**。所以能实现但是时间复杂度不符合要求。 | | +| 队列 | 单调递减的队列。遇到的问题和栈一致。 | | +| 树 | 最大二叉树能实现，但是树在内存中也是以数组的形式保存的，问题和数组一致。 | :no_entry: | + +所以说，要么用栈，要么用数组来保存sortedDatas中的数据。所以决定采用双端队列来处理sortedDatas，因为**双端队列能同时满足栈、队列的所有操作**。下一个问题便是……如何给这个双端队列进行排序。 + +堆排序、快速排序的时间复杂度是O(n lg n)；其他的线性排序算法时间复杂度是O(n)。这些都不太满足题目的要求。所以这里我想到了一种可能性：**有些数是不是没有参与排序**？如果队列中有n个数字，参与排序的数字小于n，那么排序的时间复杂度会更小的。那么，**什么样的数字可能不用参与排序呢**？max\_value方法要输出的是最大的数，所以最大的数字是一定参与排序的，即比较小的数字可以不用参与排序——我只管最大的数，其他的数字顺序对与否甚至数据的有无，都不会影响到最后的结果。 + +所以进一步的解决方案是这样的： + +每次有新的数据插入的时候，将sortedDatas中的数据从后往前跟入参比较，如果小于入参，就直接舍弃掉，直到遇到比入参大的数字时再将入参存入队列中。 + +这样的好处显而易见：小于入参的数字不会影响到最大值的输出。另一方面，队列中的数据来得比现在这个入参早，所以小于入参的数字会比这个入参更早的被删除掉。即，小于入参的数字永远不可能作为最大值背输出出来。 + +所以优化后的代码是这个样子的： + +~~~java +class MaxQueue { + Queue datas; + Deque sortedDatas; + + public MaxQueue() { + datas = new LinkedList(); + sortedDatas = new LinkedList(); + } + + public int max_value() { + if (sortedDatas.isEmpty()) { + return -1; + } + return sortedDatas.peekFirst(); + } + + public void push_back(int value) { + while (!sortedDatas.isEmpty() && sortedDatas.peekLast() < value) { + sortedDatas.pollLast(); + } + sortedDatas.offerLast(value); + datas.offer(value); + } + + public int pop_front() { + if (datas.isEmpty()) { + return -1; + } + int ans = datas.poll(); + if (ans == sortedDatas.peekFirst()) { + sortedDatas.pollFirst(); + } + return ans; + } +} + +/** + * 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(); + */ +~~~ + +此题得解。 \ No newline at end of file diff --git a/docs/LeetCode/CodingInterviews/_category_.json b/docs/LeetCode/CodingInterviews/_category_.json new file mode 100644 index 0000000..c35d1bd --- /dev/null +++ b/docs/LeetCode/CodingInterviews/_category_.json @@ -0,0 +1,4 @@ +{ + "label": "剑指Offer", + "position": 2 +} diff --git a/docs/LeetCode刷题/_category_.json b/docs/LeetCode/_category_.json similarity index 67% rename from docs/LeetCode刷题/_category_.json rename to docs/LeetCode/_category_.json index ceaadc7..b3c750c 100644 --- a/docs/LeetCode刷题/_category_.json +++ b/docs/LeetCode/_category_.json @@ -1,4 +1,4 @@ { "label": "LeetCode刷题", - "position": 4 + "position": 2 } diff --git a/docs/LeetCode刷题/intro-docs.md b/docs/LeetCode/intro-docs.md similarity index 100% rename from docs/LeetCode刷题/intro-docs.md rename to docs/LeetCode/intro-docs.md diff --git a/docs/技术文档/SpringBoot系列/_category_.json b/docs/backend-doc/SpringBoot/_category_.json similarity index 100% rename from docs/技术文档/SpringBoot系列/_category_.json rename to docs/backend-doc/SpringBoot/_category_.json diff --git a/docs/技术文档/SpringBoot系列/helloboot.md b/docs/backend-doc/SpringBoot/helloboot.md similarity index 100% rename from docs/技术文档/SpringBoot系列/helloboot.md rename to docs/backend-doc/SpringBoot/helloboot.md diff --git a/docs/技术文档/SpringCloud系列/_category_.json b/docs/backend-doc/SpringCloud/_category_.json similarity index 100% rename from docs/技术文档/SpringCloud系列/_category_.json rename to docs/backend-doc/SpringCloud/_category_.json diff --git a/docs/技术文档/SpringCloud系列/hellocloud.md b/docs/backend-doc/SpringCloud/hellocloud.md similarity index 100% rename from docs/技术文档/SpringCloud系列/hellocloud.md rename to docs/backend-doc/SpringCloud/hellocloud.md diff --git a/docs/技术文档/_category_.json b/docs/backend-doc/_category_.json similarity index 70% rename from docs/技术文档/_category_.json rename to docs/backend-doc/_category_.json index 8f4e774..fb17be5 100644 --- a/docs/技术文档/_category_.json +++ b/docs/backend-doc/_category_.json @@ -1,4 +1,4 @@ { "label": "技术文档(后端)", - "position": 2 + "position": 3 } diff --git a/docs/技术文档/intro-docs.md b/docs/backend-doc/intro-docs.md similarity index 100% rename from docs/技术文档/intro-docs.md rename to docs/backend-doc/intro-docs.md diff --git a/docs/技术文档前端/React系列/_category_.json b/docs/frontend-doc/React/_category_.json similarity index 100% rename from docs/技术文档前端/React系列/_category_.json rename to docs/frontend-doc/React/_category_.json diff --git a/docs/技术文档前端/React系列/helloreact.md b/docs/frontend-doc/React/helloreact.md similarity index 100% rename from docs/技术文档前端/React系列/helloreact.md rename to docs/frontend-doc/React/helloreact.md diff --git a/docs/技术文档前端/Vue系列/_category_.json b/docs/frontend-doc/Vue/_category_.json similarity index 100% rename from docs/技术文档前端/Vue系列/_category_.json rename to docs/frontend-doc/Vue/_category_.json diff --git a/docs/技术文档前端/Vue系列/hellovue.md b/docs/frontend-doc/Vue/hellovue.md similarity index 100% rename from docs/技术文档前端/Vue系列/hellovue.md rename to docs/frontend-doc/Vue/hellovue.md diff --git a/docs/技术文档前端/_category_.json b/docs/frontend-doc/_category_.json similarity index 70% rename from docs/技术文档前端/_category_.json rename to docs/frontend-doc/_category_.json index d1e0854..6940365 100644 --- a/docs/技术文档前端/_category_.json +++ b/docs/frontend-doc/_category_.json @@ -1,4 +1,4 @@ { "label": "技术文档(前端)", - "position": 3 + "position": 4 } diff --git a/docs/技术文档前端/intro-docs.md b/docs/frontend-doc/intro-docs.md similarity index 100% rename from docs/技术文档前端/intro-docs.md rename to docs/frontend-doc/intro-docs.md