From 587076ab113af839d828c940759a09be82598c3b Mon Sep 17 00:00:00 2001
From: Sainnhe Park <i@sainnhe.dev>
Date: Tue, 6 Dec 2022 17:24:52 +0800
Subject: [PATCH] Add impl stack queue

---
 notes/src/SUMMARY.md          |  4 +++
 notes/src/impl_stack_queue.md | 56 +++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)
 create mode 100644 notes/src/impl_stack_queue.md

diff --git a/notes/src/SUMMARY.md b/notes/src/SUMMARY.md
index 157bb92..f86fc7c 100644
--- a/notes/src/SUMMARY.md
+++ b/notes/src/SUMMARY.md
@@ -27,6 +27,10 @@
 - [KMP](./kmp.md)
 - [重复的子字符串](./repeated_substring_pattern.md)
 
+# 栈与队列
+
+- [用栈实现队列 && 用队列实现栈](./impl_stack_queue.md)
+
 # 经典代码
 
 - [合并两个有序链表](./merge_two_sorted_linked_lists.md)
diff --git a/notes/src/impl_stack_queue.md b/notes/src/impl_stack_queue.md
new file mode 100644
index 0000000..b36465c
--- /dev/null
+++ b/notes/src/impl_stack_queue.md
@@ -0,0 +1,56 @@
+# 用栈实现队列 && 用队列实现栈
+
+## 用栈实现队列
+
+[Leetcode](https://leetcode.com/problems/implement-queue-using-stacks/)
+
+「输入栈」会把输入顺序颠倒；如果把「输入栈」的元素逐个弹出放到「输出栈」，再从「输出栈」弹出元素的时候，则可以负负得正，实现了先进先出。
+
+```cpp
+#include <stack>
+
+class MyQueue {
+ public:
+  std::stack<int> *inStack, *outStack;
+
+  MyQueue() {
+    inStack = new std::stack<int>;
+    outStack = new std::stack<int>;
+  }
+
+  void transfer(void) {
+    if (outStack->empty()) {
+      while (!inStack->empty()) {
+        outStack->push(inStack->top());
+        inStack->pop();
+      }
+    }
+  }
+
+  void push(int x) { inStack->push(x); }
+
+  int pop() {
+    transfer();
+    int val = outStack->top();
+    outStack->pop();
+    return val;
+  }
+
+  int peek() {
+    transfer();
+    return outStack->top();
+  }
+
+  bool empty() { return inStack->empty() && outStack->empty(); }
+};
+```
+
+## 用队列实现栈
+
+[Leetcode](https://leetcode.com/problems/implement-stack-using-queues/)
+
+一个队列为主队列，一个为辅助队列，当入栈操作时，我们先将主队列内容导入辅助队列，然后将入栈元素放入主队列队头位置，再将辅助队列内容，依次添加进主队列即可。
+
+```cpp
+
+```