From d7e65dd894e5406d4935c777ce508cbe304bba24 Mon Sep 17 00:00:00 2001
From: Sainnhe Park <i@sainnhe.dev>
Date: Thu, 8 Dec 2022 21:05:07 +0800
Subject: [PATCH] Priority Queue

---
 include/s0239_sliding_window_maximum.hpp | 15 +++++
 notes/src/SUMMARY.md                     |  1 +
 notes/src/stack_and_queue.md             | 70 ++++++++++++++++++++++++
 src/s0239_sliding_window_maximum.cpp     | 36 ++++++++++++
 tests/s0239_sliding_window_maximum.cpp   | 19 +++++++
 5 files changed, 141 insertions(+)
 create mode 100644 include/s0239_sliding_window_maximum.hpp
 create mode 100644 notes/src/stack_and_queue.md
 create mode 100644 src/s0239_sliding_window_maximum.cpp
 create mode 100644 tests/s0239_sliding_window_maximum.cpp

diff --git a/include/s0239_sliding_window_maximum.hpp b/include/s0239_sliding_window_maximum.hpp
new file mode 100644
index 0000000..b1523e8
--- /dev/null
+++ b/include/s0239_sliding_window_maximum.hpp
@@ -0,0 +1,15 @@
+#ifndef S0239_SLIDING_WINDOW_MAXIMUM_HPP
+#define S0239_SLIDING_WINDOW_MAXIMUM_HPP
+
+#include <vector>
+#include <queue>
+#include <utility>
+
+using namespace std;
+
+class S0239 {
+ public:
+  vector<int> maxSlidingWindow(vector<int>& nums, int k);
+};
+
+#endif
diff --git a/notes/src/SUMMARY.md b/notes/src/SUMMARY.md
index f86fc7c..4e12bb0 100644
--- a/notes/src/SUMMARY.md
+++ b/notes/src/SUMMARY.md
@@ -29,6 +29,7 @@
 
 # 栈与队列
 
+- [总结](./stack_and_queue.md)
 - [用栈实现队列 && 用队列实现栈](./impl_stack_queue.md)
 
 # 经典代码
diff --git a/notes/src/stack_and_queue.md b/notes/src/stack_and_queue.md
new file mode 100644
index 0000000..58ef3ff
--- /dev/null
+++ b/notes/src/stack_and_queue.md
@@ -0,0 +1,70 @@
+# 总结
+
+## 栈
+
+使用场景：
+
+1. 需要先进后出的数据结构
+2. 匹配问题
+
+经典题目：
+
+[20. 有效的括号](https://leetcode.cn/problems/valid-parentheses/)
+
+[1047. 删除字符串中的所有相邻重复项](https://leetcode.cn/problems/remove-all-adjacent-duplicates-in-string/)
+
+## 队列
+
+使用场景：
+
+1. 先进先出的数据结构
+2. 滑动窗口
+
+### 变体：优先级队列
+
+队列中的数据以 `<priority, value>` 的形式存储，每一个 `value` 都有一个 `priority` 。
+
+当入队，我们根据 `priority` 将元素插入到队列的相应位置，队列中的元素总是按优先级升序或者降序排列。
+
+```cpp
+#include <iostream>
+#include <queue>
+#include <string>
+#include <utility>
+
+int main(int argc, const char *argv[]) {
+    // priority 为 int 类型，value 为 std::string 类型
+    std::priority_queue<std::pair<int, std::string>> q;
+    // 写入元素
+    q.push(std::make_pair(3, "Microsoft"));
+    q.push(std::make_pair(1, "Surface"));
+    q.push(std::make_pair(2, "Apple"));
+    q.push(std::make_pair(4, "MacBook"));
+    // 访问顶部元素
+    std::cout << q.top().first << q.top().second << std::endl;
+    // 删除顶部元素
+    q.pop();
+    // 检查是否为空
+    if (q.empty()) {
+        std::cout << "Empty" << std::endl;
+    } else {
+        std::cout << "Not empty" << std::endl;
+    }
+    return 0;
+}
+```
+
+输出：
+
+```text
+4MacBook
+Not empty
+```
+
+优先队列用一般用堆来实现，具有 `O(log n)` 时间复杂度的插入元素性能，`O(n)` 的初始化构造的时间复杂度。
+
+经典题目：[239. 滑动窗口最大值](https://leetcode.cn/problems/sliding-window-maximum/)
+
+### 变体：单调队列
+
+经典题目：[239. 滑动窗口最大值](https://leetcode.cn/problems/sliding-window-maximum/)
diff --git a/src/s0239_sliding_window_maximum.cpp b/src/s0239_sliding_window_maximum.cpp
new file mode 100644
index 0000000..78312e1
--- /dev/null
+++ b/src/s0239_sliding_window_maximum.cpp
@@ -0,0 +1,36 @@
+#include "s0239_sliding_window_maximum.hpp"
+#include <utility>
+
+// 优先级队列实现，每次操作的时间复杂度是 O(log(n)) ，因此总的时间复杂度是 O(n*log(n))
+// 空间复杂度是 O(n)
+vector<int> S0239::maxSlidingWindow(vector<int>& nums, int k) {
+  int len = nums.size();
+  if (len < 1 || k < 1) {
+    return {};
+  }
+  vector<int> result;
+  // 初始化优先级队列
+  priority_queue<pair<int, int>> q;
+  for (int i{0}; i < len && i < k; ++i) {
+    q.push(make_pair(nums[i], i));
+  }
+  if (k >= len) {
+    return {q.top().first};
+  } else {
+    result.push_back(q.top().first);
+  }
+  // 开始迭代
+  for (int i{1}; i + k - 1 < len; ++i) {
+    // 本轮迭代中滑动窗口的范围是 [i...i+k-1]
+    // 先把右边的元素放入队列
+    q.push(make_pair(nums[i + k - 1], i + k - 1));
+    // 确保队首元素在滑动窗口内
+    // 如果不在滑动窗口内，则弹出
+    while (q.top().second < i) {
+      q.pop();
+    }
+    // 现在队首元素就是滑动窗口内的最大值了
+    result.push_back(q.top().first);
+  }
+  return result;
+}
diff --git a/tests/s0239_sliding_window_maximum.cpp b/tests/s0239_sliding_window_maximum.cpp
new file mode 100644
index 0000000..5ab7557
--- /dev/null
+++ b/tests/s0239_sliding_window_maximum.cpp
@@ -0,0 +1,19 @@
+#include "s0239_sliding_window_maximum.hpp"
+
+#include <gtest/gtest.h>
+
+TEST(Problem239, Case1) {
+  vector<int> nums{1, 3, -1, -3, 5, 3, 6, 7};
+  int k{3};
+  vector<int> expected{3, 3, 5, 5, 6, 7};
+  S0239 solution;
+  EXPECT_EQ(solution.maxSlidingWindow(nums, k), expected);
+}
+
+TEST(Problem239, Case2) {
+  vector<int> nums{1};
+  int k{1};
+  vector<int> expected{1};
+  S0239 solution;
+  EXPECT_EQ(solution.maxSlidingWindow(nums, k), expected);
+}