From 1da6f68efb0ae0ec8b2a4db5d0e4dacb630904f7 Mon Sep 17 00:00:00 2001
From: Lam Haoyin <root@eatswap.org>
Date: Thu, 17 Feb 2022 00:09:06 +0800
Subject: [PATCH] add: 220216

---
 2202/220216.cpp     | 59 +++++++++++++++++++++++++++++++++++++++++++++
 2202/CMakeLists.txt |  2 +-
 2 files changed, 60 insertions(+), 1 deletion(-)
 create mode 100644 2202/220216.cpp

diff --git a/2202/220216.cpp b/2202/220216.cpp
new file mode 100644
index 0000000..bf52e81
--- /dev/null
+++ b/2202/220216.cpp
@@ -0,0 +1,59 @@
+#include <iostream>
+
+/**
+ * Definition for singly-linked list.
+ */
+struct ListNode {
+	int val;
+	ListNode* next;
+
+	explicit ListNode(int x = 0, ListNode* next = nullptr) : val(x), next(next) {}
+};
+
+ListNode* construct(int x) {
+	return new ListNode(x);
+}
+
+template<typename... Ts>
+ListNode* construct(int x, Ts... xs) {
+	return new ListNode(x, construct(xs...));
+}
+
+class Solution {
+public:
+	static ListNode* swapPairs(ListNode* head) {
+		ListNode ret(0, head);
+		auto* ptr = &ret;
+		while (ptr) {
+			ListNode* ptrN = ptr->next;
+			if (!ptrN)
+				break;
+
+			ListNode* ptrNN = ptrN->next;
+			if (!ptrNN)
+				break;
+
+			// ptr --> ptrN --> ptrNN --> ptrNNN
+			ListNode* ptrNNN = ptrNN->next;
+
+			// ptr is previous node
+			// swap ptrN and ptrNN.
+			ptrNN->next = ptrN;
+			ptr->next = ptrNN;
+			ptrN->next = ptrNNN;
+
+			// ptr --> ptrNN --> ptrN --> ptrNNN
+			ptr = ptrN;
+		}
+		return ret.next;
+	}
+};
+
+int main() {
+	auto* head = construct(1, 2, 3, 4, 5, 6);
+	head = Solution::swapPairs(head);
+	for (auto* ptr = head; ptr; ptr = ptr->next) {
+		std::printf("%d ", ptr->val);
+	}
+	return 0;
+}
diff --git a/2202/CMakeLists.txt b/2202/CMakeLists.txt
index 7d0ba3b..5b1fc4f 100644
--- a/2202/CMakeLists.txt
+++ b/2202/CMakeLists.txt
@@ -3,4 +3,4 @@ PROJECT(2202)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2202 220215.cpp)
+ADD_EXECUTABLE(2202 220216.cpp)