GuilinDev

Lc0814

05 August 2008

814 Binary Tree Pruning

Given the 

1

root
of a binary tree, return the same tree where every subtree (of the given tree) not containing a 
1

1
has been removed.

A subtree of a node 

1

node
is 
1

node
plus every node that is a descendant of 
1

node
.

Example 1:

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3
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5

Input: root = [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:

1
2

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

Example 3:

1
2

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

Constraints:

  • The number of nodes in the tree is in the range 
    1

    [1, 200]
    .
  • 1

    Node.val
    is either 
    1

    0
    or 
    1

    1
    .

代码

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public TreeNode pruneTree(TreeNode root) {
        if (root == null) {
            return root;
        }
        
        root.left = pruneTree(root.left);  //null
        root.right = pruneTree(root.right);
        
        if (root.val == 1 || root.left != null || root.right != null) {
            return root;
        }
        
        return null;
    }
}
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