814. Binary Tree Pruning.md

814. Binary Tree Pruning

We are given the head node root of a binary tree, where additionally every node's value is either a 0 or a 1.

Return the same tree where every subtree (of the given tree) not containing a 1 has been removed.

(Recall that the subtree of a node X is X, plus every node that is a descendant of X.)

Example 1:

Input: [1,null,0,0,1]
Output: [1,null,0,null,1]

Explanation: 
Only the red nodes satisfy the property "every subtree not containing a 1".
The diagram on the right represents the answer.

Example 2:

Input: [1,0,1,0,0,0,1]
Output: [1,null,1,null,1]

Example 3:

Input: [1,1,0,1,1,0,1,0]
Output: [1,1,0,1,1,null,1]

Note:

• The binary tree will have at most 100 nodes.
• The value of each node will only be 0 or 1.

Solution

• java

  • mine Runtime: 0 ms, faster than 100.00% of Java

  /**
   * Definition for a binary tree node.
   * public class TreeNode {
   *     int val;
   *     TreeNode left;
   *     TreeNode right;
   *     TreeNode(int x) { val = x; }
   * }
   */
  class Solution {
      public TreeNode pruneTree(TreeNode node) {
         if(node == null){
              return node;
          }
  
          node.left = pruneTree(node.left);
          node.right = pruneTree(node.right);
  
          if(node.val == 0 && node.left == null && node.right == null){
              node = null;
          }
          return node;
      }
  }