【LeetCode】114. Flatten Binary Tree to Linked List

本文详细介绍了一种算法,该算法能将任意给定的二叉树通过原地操作转换为链表,转换遵循前序遍历顺序。文章通过实例演示了如何将二叉树的左子树连接到右子树,最终形成链表结构。

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Given a binary tree, flatten it to a linked list in-place.

For example, given the following tree:

    1
   / \
  2   5
 / \   \
3   4   6

The flattened tree should look like:

1
 \
  2
   \
    3
     \
      4
       \
        5
         \
          6

给一个二叉树,要求按前序遍历的顺序把二叉树变成一个链表。

step1:指针指向根节点,首先将根节点的左子树挂在根节点的右子树上,左子树前序遍历最后一个元素(即4)指向原右子树的根节点5,根节点左子树指向空。

    1
     \
      2     
     / \   
    3   4
         \
          5
           \
            6

step2:此时指针指向根节点的右子树根节点2,重复step1,也就是将2的左子树挂在2的右子树上,左子树最后一个元素连接2的原右子树根节点5,2的左指针指向空。

    1
     \
      2     
       \   
        3
         \
          4
           \
            5
             \
              6

代码如下:

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void flatten(TreeNode* root) {
        while(root!=NULL){
            if(root->left!=NULL){
                TreeNode* curr=root->left;
                while(curr->right!=NULL)
                    curr=curr->right;
                curr->right=root->right;
                root->right=root->left;
                root->left=NULL;
            }
            root=root->right;
        }
       
    }
};

耐心些,按照例子仔细划分一遍。

1. Two Sum 2. Add Two Numbers 3. Longest Substring Without Repeating Characters 4. Median of Two Sorted Arrays 5. Longest Palindromic Substring 6. ZigZag Conversion 7. Reverse Integer 8. String to Integer (atoi) 9. Palindrome Number 10. Regular Expression Matching 11. Container With Most Water 12. Integer to Roman 13. Roman to Integer 14. Longest Common Prefix 15. 3Sum 16. 3Sum Closest 17. Letter Combinations of a Phone Number 18. 4Sum 19. Remove Nth Node From End of List 20. Valid Parentheses 21. Merge Two Sorted Lists 22. Generate Parentheses 23. Swap Nodes in Pairs 24. Reverse Nodes in k-Group 25. Remove Duplicates from Sorted Array 26. Remove Element 27. Implement strStr() 28. Divide Two Integers 29. Substring with Concatenation of All Words 30. Next Permutation 31. Longest Valid Parentheses 32. Search in Rotated Sorted Array 33. Search for a Range 34. Find First and Last Position of Element in Sorted Array 35. Valid Sudoku 36. Sudoku Solver 37. Count and Say 38. Combination Sum 39. Combination Sum II 40. First Missing Positive 41. Trapping Rain Water 42. Jump Game 43. Merge Intervals 44. Insert Interval 45. Unique Paths 46. Minimum Path Sum 47. Climbing Stairs 48. Permutations 49. Permutations II 50. Rotate Image 51. Group Anagrams 52. Pow(x, n) 53. Maximum Subarray 54. Spiral Matrix 55. Jump Game II 56. Merge k Sorted Lists 57. Insertion Sort List 58. Sort List 59. Largest Rectangle in Histogram 60. Valid Number 61. Word Search 62. Minimum Window Substring 63. Unique Binary Search Trees 64. Unique Binary Search Trees II 65. Interleaving String 66. Maximum Product Subarray 67. Binary Tree Inorder Traversal 68. Binary Tree Preorder Traversal 69. Binary Tree Postorder Traversal 70. Flatten Binary Tree to Linked List 71. Construct Binary Tree from Preorder and Inorder Traversal 72. Construct Binary Tree from Inorder and Postorder Traversal 73. Binary Tree Level Order Traversal 74. Binary Tree Zigzag Level Order Traversal 75. Convert Sorted Array to Binary Search Tree 76. Convert Sorted List to Binary Search Tree 77. Recover Binary Search Tree 78. Sum Root to Leaf Numbers 79. Path Sum 80. Path Sum II 81. Binary Tree Maximum Path Sum 82. Populating Next Right Pointers in Each Node 83. Populating Next Right Pointers in Each Node II 84. Reverse Linked List 85. Reverse Linked List II 86. Partition List 87. Rotate List 88. Remove Duplicates from Sorted List 89. Remove Duplicates from Sorted List II 90. Intersection of Two Linked Lists 91. Linked List Cycle 92. Linked List Cycle II 93. Reorder List 94. Binary Tree Upside Down 95. Binary Tree Right Side View 96. Palindrome Linked List 97. Convert Binary Search Tree to Sorted Doubly Linked List 98. Lowest Common Ancestor of a Binary Tree 99. Lowest Common Ancestor of a Binary Search Tree 100. Binary Tree Level Order Traversal II
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