Linked List

1.Easy

(21)Merge Two Sorted Lists

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class ListNode(object):
def __init__(self, val=0, next=None):
self.val = val
self.next = next

class Solution(object):
def mergeTwoLists(self, l1, l2):
dummy = cur = ListNode(1)
while l1 and l2:
if l1.val < l2.val:
cur.next = l1
l1 = l1.next
else:
cur.next = l2
l2 = l2.next
cur = cur.next
cur.next = l1 or l2
return dummy.next

(141)Linked List Cycle

(206)Reverse Linked List

2.Medium

(5)Longest Palindromic Substring

(19)Remove Nth Node From End of List

(114)Flatten Binary Tree to Linked List

(142)Linked List Cycle II

(146)LRU Cache

(148)Sort List

3.Hard

(23)Merge k Sorted Lists