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[其他] Swap Nodes in Binary tree of every k’th level

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黑白颠倒 发表于 3 天前
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Given a binary tree and integer value k, the task is to swap sibling nodes of every k’th level where k >= 1.
  Examples:
  1. Input :  k = 2  and Root of below tree                     
  2.       1             Level 1
  3.     /   \
  4.    2     3          Level 2
  5. /     /   \
  6. 4     7     8       Level 3

  7. Output : Root of the following modified tree
  8.       1
  9.     /   \
  10.    3     2
  11. /  \   /  
  12. 7    8  4
  13. Explanation : We need to swap left and right sibling
  14.               every second level. There is only one
  15.               even level with nodes to be swapped are
  16.               2 and 3.


  17. Input : k = 1 and Root of following tree
  18.             
  19.        1          Level 1
  20.      /   \
  21.     2     3       Level 2
  22.   /  \
  23. 4    5           Level 3
  24. Output : Root of the following modified tree
  25.        1
  26.      /   \
  27.     3     2
  28.          /  \
  29.         5    4
  30. Since k is 1, we need to swap sibling nodes of
  31. all levels.
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A    simple solutionof this problem is that for each is to find sibling nodes for each multiple of k and swap them.  
  An    efficient solutionis to keep track of level number in recursive calls. And for every node being visited, check if level number of its children is a multiple of k. If yes, then swap the two children of the node. Else, recur for left and right children.  
  Below is C++ implementation of above idea
  1. // c++ program swap nodes
  2. #include<bits/stdc++.h>
  3. using namespace std;

  4. // A Binary Tree Node
  5. struct Node
  6. {
  7.     int data;
  8.     struct Node *left, *right;
  9. };

  10. // function to create a new tree node
  11. Node* newNode(int data)
  12. {
  13.     Node *temp = new Node;
  14.     temp->data = data;
  15.     temp->left = temp->right = NULL;
  16.     return temp;
  17. }

  18. // swap two Node
  19. void Swap( Node **a , Node **b)
  20. {
  21.     Node * temp = *a;
  22.     *a = *b;
  23.     *b = temp;
  24. }

  25. // A utility function swap left- node & right node of tree
  26. // of every k'th level
  27. void swapEveryKLevelUtil( Node *root, int level, int k)
  28. {
  29.     // base case
  30.     if (root== NULL ||
  31.             (root->left==NULL && root->right==NULL) )
  32.         return ;

  33.     //if current level + 1  is present in swap vector
  34.     //then we swap left & right node
  35.     if ( (level + 1) % k == 0)
  36.         Swap(&root->left, &root->right);

  37.     // Recur for left and right subtrees
  38.     swapEveryKLevelUtil(root->left, level+1, k);
  39.     swapEveryKLevelUtil(root->right, level+1, k);
  40. }

  41. // This function mainly calls recursive function
  42. // swapEveryKLevelUtil()
  43. void swapEveryKLevel(Node *root, int k)
  44. {
  45.     // call swapEveryKLevelUtil function with
  46.     // initial level as 1.
  47.     swapEveryKLevelUtil(root, 1, k);
  48. }

  49. // Utility method for inorder tree traversal
  50. void inorder(Node *root)
  51. {
  52.     if (root == NULL)
  53.         return;
  54.     inorder(root->left);
  55.     cout << root->data << " ";
  56.     inorder(root->right);
  57. }

  58. // Driver Code
  59. int main()
  60. {
  61.     /*    1
  62.         /   \
  63.        2     3
  64.      /      /  \
  65.     4      7    8   */
  66.     struct Node *root = newNode(1);
  67.     root->left = newNode(2);
  68.     root->right = newNode(3);
  69.     root->left->left = newNode(4);
  70.     root->right->right = newNode(8);
  71.     root->right->left = newNode(7);

  72.     int k = 2;
  73.     cout << "Before swap node :"<<endl;
  74.     inorder(root);

  75.     swapEveryKLevel(root, k);

  76.     cout << "\nAfter swap Node :" << endl;
  77.     inorder(root);
  78.     return 0;
  79. }
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Output:

  1. Before swap node :
  2. 4 2 1 7 3 8
  3. After swap Node :
  4. 7 3 8 1 4 2
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This article is contributed by    Nishant_singh(pintu). If you like GeeksforGeeks and would like to contribute, you can also write an article using    contribute.geeksforgeeks.orgor mail your article to [email protected] See your article appearing on the GeeksforGeeks main page and help other Geeks.  
  Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
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