206. 反转链表 (二刷)

Author: w2xi

vs-lt/206.反转链表.js

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+/*
+ * @lc app=leetcode.cn id=206 lang=javascript
+ *
+ * [206] 反转链表
+ */
+
+// @lc code=start
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+var reverseList = function(head) {
+  // 递归
+
+  // 1 -> 2 -> 3 -> 4 -> 5
+  // =>
+  // 5 -> 4 -> 3 -> 2 -> 1
+
+  const reverseNode = (curr, prev) => {
+    if (curr) {
+      let next = curr.next;
+      curr.next = prev;
+      return reverseNode(next, curr);
+    } else {
+      return prev;
+    }
+  }
+
+  return reverseNode(head, null);
+
+  // 双指针
+
+  // let next = null; // 保存 curr 的下一个节点
+  // let prev = null;
+  // let curr = head;
+
+  // while (curr) {
+  //   next = curr.next
+  //   curr.next = prev;
+  //   prev = curr;
+  //   curr = next;
+  // }
+
+  // return prev;
+};
+// @lc code=end
+