Как удалить наное дерево? каждый узел имеет родительский указатель

Question

Структура узла ниже.

struct node
{
   int data;
   int noofchilds;
   node *child[n];
   node *parent;
 };

Я был бы признателен за рекурсивный и нерекурсивный подходы.

Answer 1

Нерекурсивная версия:

struct node {
    struct node *parent;
    unsigned nchild;
    struct node *child[XXX];
    int data;
    };

void deltree(struct node *np)
{
struct node *par;

while (np) {
        /* if this node has any children, start by
        ** "descending" to the highest numbered child and kill that first.
        */
        if (np->nchild--) {
                np = np->child[np->nchild];
                continue;
                }
        /* when we arrive here, *np has no more children left,
        ** so kill it, and step up to its parent
        */
        par = node->parent;
        // if np->child was obtained via malloc() uncomment next line
        // free (np->child);
        free (np);
        np = par;
        }
return;
}

Answer 2

Итерационный алгоритм:

Start at the parent node.

Then do the following actions as long as possible:
   if the current node has one or more children: 
      set one of the children nodes as the (next) current node
   else
      delete the current node and use its parent as the (next) current node.
      if the current node was the root node (which has no parent), stop.

Answer 3

Удалите узел и рекурсивно удалите его дочерние элементы.

Если вам нужно удалить полное дерево (как кажется, ваш вопрос), родительский указатель не имеет значения (и удаляется при удалении самого узла).

Answer 4

Надеюсь, поможет.

      // Program to delete all the nodes of a n-Ary tree ~ coded by Hiren
#include <iostream>
#include <vector>
#include <queue>
using namespace std;

// Tree template
struct Node {
    int val;
    vector<Node*> children;

    // Init constructor
    Node(int val) {
        this->val = val;
    };
};

// Method to print the tree using preOrder traversal
void printTree(Node* root) {
    if(root) {
        cout<<root->val<<' ';
        for(auto childNode : root->children) {
            printTree(childNode);
        }
    }
}

// #1 Method to delete all the nodes of the n-Ary tree using bfs - O(N) & O(M) : Where M is the maximum number of nodes at any level
void deleteAllNodes(Node*& root) {
    // Edge case: When the tree is empty
    if(!root)
        return;

    queue<Node*> q;
    q.push(root);

    while(!q.empty()) {
        // Take the front node of the queue
        root = q.front(); q.pop();
        
        // Store all its childrens to the queue
        for(auto childNode : root->children) {
            q.push(childNode);
        }

        // Ensurely set the node to nullptr and than delete it else a segmentation fault can occur
        root = nullptr;
        delete root;
    }

}

// #2 Method to delete all the nodes of the n-Ary tree using dfs - O(N) & O(H) : Where H let be the maximum height of the tree
void deleteAllNodes_(Node*& root) {
    // Edge case: When the tree is empty
    if(!root)
        return;

    // Visit each of the children one by one
    for(auto childNode : root->children) {
        deleteAllNodes_(childNode);
    }

    // Ensurely set the node to nullptr and than delete it else a segmentation fault can occur
    root = nullptr; 
    delete root;
}

// Driver code
int main() {
    // Creating tree, connecting nodes and initializing their data
    Node* root = new Node(3);
    root->children.push_back(new Node(5));
    root->children.push_back(new Node(1));
    root->children[0]->children.push_back(new Node(6));
    root->children[0]->children.push_back(new Node(2));
    root->children[0]->children[0]->children.push_back(new Node(10));
    root->children[0]->children[0]->children.push_back(new Node(11));
    root->children[0]->children[0]->children.push_back(new Node(12));
    root->children[0]->children[1]->children.push_back(new Node(7));
    root->children[0]->children[1]->children.push_back(new Node(4));

    // Print call
    printTree(root); cout<<'\n';

    // Deletion call
    deleteAllNodes_(root);    

    return 0;
}
// Link: https://stackoverflow.com/questions/9414290/how-to-delete-a-nary-tree-each-node-has-a-parent-pointer-too-in-it