🔢
Algorithms & Data
  • Overview
    • 1. Sort
      • Selection Sort
      • Bubble Sort
      • Insertion Sort
        • Insertion Sort:: singly linked list
          • Recursive
          • Using Array O(N), O(N)
          • Using Iteration O(N), O(1)
      • Quick Sort
      • Merge Sort
      • Heap Sort
      • Counting Sort
        • Counting Sort
          • Sort a String
        • Bucket Sort
        • Radix Sort
      • Topological Sort
    • 2. Data Structures
      • Array
      • Stack
      • Queue
      • Tree
        • PreOrder, InOrder, PostOrder
          • Transfer between each
          • Traverse
        • Binary Tree
          • Binary Search Tree
      • Graph
        • Data Structure
        • Traverse Graph
        • Detect a cycle in a Graph
          • DFS *
            • undirected clean code
          • Union Find
          • Count edges - undirected only
      • Linked List
      • Trie
        • Javascript
        • Java
      • Union Find
        • Detect Cycle with Disjoint-set Union Find
        • Kruskal Algorithm
      • Heap
      • Matrix
      • Union Find: Disjoint Set
    • 3. How to construct Algorithm? Paradigm
      • Greedy Algorithm
        • Prim
        • Dijkstra
        • Prim vs Dijkstra
      • Dynamic Planning Techique
      • Dynamic Planning
      • Divide And Conquer
      • Brute force
      • Shortest path
        • BFS
        • Dijkstra algorithm: directed, shortest path
      • MST (Minimum Spanning Tree)
        • Prim vs Digkstra
        • Prim, Kruskal Why? only undirected graph?
        • Kruskal's Algorithm: undirected
        • Prim's Algorithm: undirected
  • Algorithm Problems
    • Problem Sources
    • AlgoExpert
      • Hardest
        • Merge Sort
      • Hard
        • Prim’s Algorithm
        • Dijkstra’s Algorithm
        • Kruskal’s algorithm vs Prim’s algorithm
        • Topological Sort
        • Max Sum Increasing Subsequence
        • Find Nodes Distance K
        • Max Path Sum In Binary Tree
        • Validate Three Nodes
        • Same BST ?
        • Zigzag Traverse
        • Min Rewards
        • Largest Range
        • Subarray Sort
        • Four Number Sum
      • Medium
        • Missing Numbers
        • Beat Seat
        • Suffix Trie Construction
        • One Edit
        • Minimum Characters For Words
        • Reverse Words in String
        • Valid IP Addresses
        • Group Anagrams
        • Longest Palindromic Substring
        • Next Greater Element
        • Sort Stack ⇒ recursive good -
        • Sunset Views
        • Balanced Brackets
        • Min Max Stack Construction
        • Three Number Sort ⇒ counting sort or radix sort ⇒ three pointer with in-place swap
        • Staircase Traversal ⇒ it is like the number of ways to change
        • Phone Number Mnemonics ⇒ can use word and index to create each case without concatenation
        • Power Set
        • Permutations -
        • Merging LinkedLists
        • Sum Of Linked Lists -
        • Remove Kth Node From End -
        • Linked List Construction - Doubly Linked List ?
        • Min Heap Construction
        • Valid Starting City
        • Task Assignment - use two pointer
        • Two Colorable - Graph
        • Minimum Passes Of Matrix
        • Cycle in Graph -
        • Remove Islands -
        • Youngest Common Ancestor
        • River Sizes -
        • Breadth First Search
        • Single Cycle Check
        • Union Find
        • Stable Internships
        • Kadane’s Algorithm
        • Levenshtein Distance
        • Min Number Of Coins For Change
        • Number Of Ways To Make Change
        • Number Of Ways To Traverse Graph
        • Max Subset Sum No Adjacent
        • Symmetrical Tree
        • Merge Binary Trees
        • Height Balanced Binary Tree
        • Find Successor
        • Binary Tree Diameter
        • Invert Binary Tree
        • Reconstruct Bst
        • Find Kth Largest Value In Bst
        • Min Height BST
        • BST Traversal
        • Validate Bst
        • BST Construction
        • Zero Sum Subarray + find indices of sub array
        • Merge Overlapping Intervals
        • First Duplicate Number
        • Array of Products
        • Longest Peak
        • Spiral Traverse
        • Monotonic Array
        • Move Element To End
        • Smallest Difference
        • Three Number Sum
      • Easy
        • Middle Node
        • Evaluate Expression Tree
        • Insertion Sort
        • Semordnilap
        • First Non Repeating Character
        • Generate Document
        • Run Length Encoding
        • Caesar Cipher Encryptor
        • Palindrome Check
        • Selection Sort
        • Bubble Sort
        • Find Three Largest Sum
        • Binary Search
        • Product Sum
        • Nth Fibonacci
        • Remove Duplicates From LinkedList
        • Tandem Bicycle
        • Class Photos
        • Minimum Waiting Time
        • Depth-first Search
        • Node Depths
        • Branch Sums
        • Find Closest Value In Bst
        • Non Constructible Change
        • Tournament Winner
        • Sorted Squared Array
        • Validate Subsequences
        • Two Number Sum
    • Daily Algorithms
      • 1. Topological Sort
      • 2. MST- Prim, Kruskal
      • 3. Cycle in a Graph
        • [Algo] Cycle in Graph (directed)
      • 4. Maximum sub array sum
        • Problem
        • Solutions
          • Brute Force
          • Divide And Conquer
          • Kadane's Algorithm - Dynamic
        • Empty Array allowed
        • Empty Array not allowed
        • Empty Array Not Allowed + circular
          • Double array:: O(N), O(N)
          • minimum subarray:: O(N), O(1)
      • 5. Detect a Cycle in a graph with a disjoint set (Union Find)
      • 6. Kruskal's Algorithm - Union Find
      • 7. Prim's Algorithm - Priority Queue
      • 8. Sort Array nlogn
      • 9. Shortest path - BFS
      • 10. Dijkstra algorithm
      • 11. Minimum spanning tree - points
      • 12. Minimum depth in a binary tree
      • 13. [Counting Sort]: H-index
      • 14. [shortest path]: Floyd-Warshall
      • 15. [Linked List]: reverse list
      • 16. [Linked List]: swap nodes in pairs
      • 17.[Linked List]: Merge k Sorted Lists
      • 18.[Linked list]:234. Palindrome Linked List
      • 19. [Linked List]: Linked List Cycle
      • 20. [Linked List] Reverse Linked List II
      • 21. [Linked List] sort a list - asc
      • 22. [Sort] Quick Sort
      • 23. [matrix] Spiral Matrix
      • 24. [matrix] Number of Islands
      • 25. [matrix] Valid Sudoku
      • 26. [matrix] Sudoku Solver
  • Top 75 LeetCode Questions to Save Your Time
    • Source
    • Problems
      • Interval
        • 56. Merge Intervals
        • 435. Non-overlapping Intervals
        • x 57. Insert Interval
      • Heap
        • x 295. Find Median from Data Stream
        • 347. Top K Frequent Elements
        • 23. Merge k Sorted Lists
      • Array
        • Untitled
        • 10. 11. Container With Most Water
        • 9. 15. 3Sum
        • 8. 33. Search in Rotated Sorted Array
        • 7. 153. Find Minimum in Rotated Sorted Array
        • x 6. 152. Maximum Product Subarray
        • 5. 53. Maximum Subarray
        • 4. 238. Product of Array Except Self
        • 1. Two Sums
        • 2. Best Time to Buy and Sell Stock
        • 3. Contains Duplicate
      • Binary
        • 190. Reverse Bits
        • 268. Missing Number
        • x 338. Counting Bits
        • 12. 191. Number of 1 Bits
        • 11. 371. Sum of Two Integers
      • Graph
        • x 417. Pacific Atlantic Water Flow
        • x 128. Longest Consecutive Sequence
        • 207. Course Schedule
        • 133. Clone Graph
        • 200. Number of Islands
      • Tree
        • x 297. Serialize and Deserialize Binary Tree
        • x 105. Construct Binary Tree from Preorder and Inorder Traversal
        • x 212. Word Search II
        • 211. Design Add and Search Words Data Structure
        • 208. Implement Trie (Prefix Tree)
        • 235. Lowest Common Ancestor of a Binary Search Tree
        • 230. Kth Smallest Element in a BST
        • 98. Validate Binary Search Tree
        • 572. Subtree of Another Tree
        • 297. Serialize and Deserialize Binary Tree ?
        • 102. Binary Tree Level Order Traversal
        • 124. Binary Tree Maximum Path Sum
        • 226. Invert Binary Tree
        • 100. Same Tree
        • 104. Maximum Depth of Binary Tree
      • Dynamic Programming
        • x 62. Unique Paths
        • x91. Decode Ways
        • 55. Jump Game
        • x 213. House Robber II
        • 198. House Robber
        • 377. Combination Sum IV
        • x 139. Word Break
        • 1143. Longest Common Subsequence
        • 300. Longest Increasing Subsequence
        • 322. Coin Change
        • 70. Climbing Stairs
        • 2023 0709 39. Combination Sum
      • String
        • x 76. Minimum Window Substring
        • 647. Palindromic Substrings
        • x 5. Longest Palindromic Substring
        • 125. Valid Palindrome
        • 20. Valid Parentheses
        • 49. Group Anagrams
        • 242. Valid Anagram
        • 5. Longest Palindromic Substring
        • 3. Longest Substring Without Repeating Characters
      • Matrix
        • x 48. Rotate Image
        • 79. Word Search
        • x 73. Set Matrix Zeroes
        • 54. Spiral Matrix
      • Linked List
        • 143. Reorder List
        • 19. Remove Nth Node From End of List
        • 23. Merge k Sorted Lists
        • 21. Merge Two Sorted Lists
        • 141. Linked List Cycle
        • 206. Reverse Linked List
  • Tip
    • Page 2
    • LinkedList
Powered by GitBook
On this page
  1. Algorithm Problems
  2. Daily Algorithms

16. [Linked List]: swap nodes in pairs

Previous15. [Linked List]: reverse listNext17.[Linked List]: Merge k Sorted Lists

Last updated 1 year ago

24. Swap Nodes in Pairs

Medium10.6K387Companies

Given a linked list, swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list's nodes (i.e., only nodes themselves may be changed.)

Example 1:

Input: head = [1,2,3,4]
Output: [2,1,4,3]

Example 2:

Input: head = []
Output: []

Example 3:

Input: head = [1]
Output: [1]

Constraints:

  • The number of nodes in the list is in the range [0, 100].

  • 0 <= Node.val <= 100

/**
 * 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 swapPairs = function(head) {
    const dummy = new ListNode(-1, null);
    dummy.next = head;

    let prev = dummy;
    let curr = head;

    while (curr !== null && curr.next !== null) {
        const next = curr.next;
        const nextnext = curr.next.next;

        prev.next = next;
        next.next = curr;
        curr.next = nextnext;
        
        prev = curr;
        curr = nextnext;
    }

    return dummy.next;
};

LogoLoading...LeetCode