Solution of LeetCode plan Solution # Title Difficulty TimeComplexity SpaceComplexity 0001 Two Sum Easy O(n) O(n) 0002 Add Two Numbers Medium O(n) O(n) 0009 Palindrome Number Easy O(logn) O(1) 0015 3Sum Medium 0020 Valid Parentheses Easy 0021 Merge Two Sorted Lists Easy O(n) O(1) 0025 Reverse Nodes In K-Group Hard 0026 Remove Duplicates from Sorted Array Easy 0028 Implement strStr() Easy O(n) O(n) 0048 Rotate Image Medium 0054 Spiral Matrix Medium 0055 Jump Game Medium 0056 Merge Intervals Medium 0058 Length of Last Word Easy 0091 Decode Ways Medium 0121 Best Time to Buy and Sell Stock Easy 0125 Valid Palindrome Easy 0144 Binary Tree Preorder Traversal Medium 0155 Min Stack Easy 0203 Remove Linked List Elements Easy 0206 Reverse Linked List Easy O(n) O(1) 0225 Implement Stack Use Queue Easy O(n) O(n) 0240 Count Primes Medium 0242 Valid Anagram Easy O(n) O(n) 0264 Ugly Number II Medium 0328 Odd Even Linked List Medium O(n) O(1) 0344 Reverse String Easy 0448 Find All Numbers Disappeared in an Array Easy 0589 N-ary Tree Preorder Traversal Easy 0590 N-ary Tree Postorder Traversal Easy 0739 Daily Temperatures Medium 0876 Middle of the Linked List Easy 1047 Remove All Adjacent Duplicates In String Easy 1108 Defanging an IP Address Easy 1502 Can Make Arithmetic Progression From Sequence Easy O(n) O(1)