Binary Tree Pruning in C++

Suppose we have the head node root of a binary tree, where additionally every node's value is either a 0 or a 1. We have to find the same tree where every subtree not containing a 1 has been deleted. So if the tree is like −

To solve this, we will follow these steps −

• Define a recursive method solve(), this will take the node. the method will be like −

• If node is null, then return null

• left of node := solve(left of node)

• right of node := solve(right of node)

• if left of node is null and right of node is also null and node value is 0, then return null

• return node

Let us see the following implementation to get better understanding −

Example

 Live Demo

#include <bits/stdc++.h>
using namespace std;
class TreeNode{
   public:
   int val;
   TreeNode *left, *right;
   TreeNode(int data){
      val = data;
      left = NULL;
      right = NULL;
   }
};
void insert(TreeNode **root, int val){
   queue<TreeNode*> q;
   q.push(*root);
   while(q.size()){
      TreeNode *temp = q.front();
      q.pop();
      if(!temp->left){
         temp->left = new TreeNode(val);
         return;
      }else{
         q.push(temp->left);
      }
      if(!temp->right){
         temp->right = new TreeNode(val);
         return;
      }else{
         q.push(temp->right);
      }
   }
}
TreeNode *make_tree(vector<int> v){
   TreeNode *root = new TreeNode(v[0]);
   for(int i = 1; i<v.size(); i++){
      insert(&root, v[i]);
   }
   return root;
}
void tree_level_trav(TreeNode*root){
   if (root == NULL) return;
   cout << "[";
   queue<TreeNode *> q;
   TreeNode *curr;
   q.push(root);
   q.push(NULL);
   while (q.size() > 1) {
      curr = q.front();
      q.pop();
      if (curr == NULL){
         q.push(NULL);
      } else {
         if(curr->left)
            q.push(curr->left);
         if(curr->right)
            q.push(curr->right);
         if(curr == NULL){
            cout << "null" << ", ";
         }else{
            cout << curr->val << ", ";
         }  
      }
   }
   cout << "]"<<endl;
}
class Solution {
   public:
   TreeNode* pruneTree(TreeNode* node) {
      if(!node)return NULL;
      node->left = pruneTree(node->left);
      node->right = pruneTree(node->right);
      if(!node->left && !node->right && !node->val){
         return NULL;
      }
      return node;
   }
};
main(){
   vector<int> v = {1,1,0,1,1,0,1,0};
   TreeNode *root = make_tree(v);
   Solution ob;
   tree_level_trav(ob.pruneTree(root));
}

Input

[1,1,0,1,1,0,1,0]

Output

[1, 1, 0, 1, 1, 1, ]