814. Binary Tree Pruning
Tags: ‘Tree’
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
0or1.
Solution
// Recursive
// 1. what should the function return(functionality)
// 2. what is the end case
class Solution {
public TreeNode pruneTree(TreeNode root) {
if (root == null) return null;
root.left = pruneTree(root.left); // prune children first
root.right = pruneTree(root.right);
if (root.left == null && root.right == null && root.val == 0) return null; // prune current
return root;
}
}