814

814. Binary Tree Pruning (Medium)

Given the root of a binary tree, return the same tree where every subtree (of the given tree) not containing a 1 has been removed.

A subtree of a node node is node plus every node that is a descendant of node.

 

Example 1:

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:

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

Example 3:

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, 200].
• Node.val is either 0 or 1.

Companies:
Amazon, Google

Related Topics:
Tree, Depth-First Search, Binary Tree

Solution 1.

// OJ: https://leetcode.com/problems/binary-tree-pruning/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(logN)
class Solution {
public:
    TreeNode* pruneTree(TreeNode* root) {
        if (!root) return NULL;
        root->left = pruneTree(root->left);
        root->right = pruneTree(root->right);
        return root->left || root->right || root->val ? root : NULL;
    }
};