add 206. 反转链表

Author: ScoutYin

leetcode/链表/206. 反转链表/reverseList1.js

@@ -0,0 +1,28 @@
+// LeetCode 原题：206. 反转链表
+// https://leetcode-cn.com/problems/reverse-linked-list/
+
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * 递归法
+ * 时间复杂度 O(n)
+ * 空间复杂度 O(n) 递归深度
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+var reverseList = function (head) {
+	// 递归终止条件
+	if (head === null || head.next === null) {
+		return head;
+	}
+	const node = reverseList(head.next);
+	// 反转
+	head.next.next = head;
+	head.next = null;
+	return node;
+};

leetcode/链表/206. 反转链表/reverseList2.js

@@ -0,0 +1,29 @@
+// LeetCode 原题：206. 反转链表
+// https://leetcode-cn.com/problems/reverse-linked-list/
+
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * 迭代法
+ * 时间复杂度 O(n)
+ * 空间复杂度 O(1)
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+var reverseList = function (head) {
+	let prev = null;
+	let cur = head;
+	let next;
+	while (cur) {
+		next = cur.next;
+		cur.next = prev;
+		prev = cur;
+		cur = next;
+	}
+	return prev;
+};