题目大意：把不含有1的节点的子树全部删除。

https://leetcode.com/problems/binary-tree-pruning/description/

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]

Solution: Recursion

Time complexity: O(n)

Space complexity: O(h)

C++

// Author: Huahua
// Running time: 6 ms
class Solution {
public:
  TreeNode* pruneTree(TreeNode* root) {
    if (!root) return root;
    root->left = pruneTree(root->left);
    root->right = pruneTree(root->right);
    if (root->val == 1 || root->left || root->right)
      return root;
    delete root;
    return nullptr;
  }
};

Java

// Author: Huahua
// Running time: 2 ms
class Solution {
  public TreeNode pruneTree(TreeNode root) {
    if (root == null) return root;
    root.left = pruneTree(root.left);
    root.right = pruneTree(root.right);
    return (root.val == 1 || root.left != null || root.right != null) ? root : null;
  }
}

Python3

// Author: Huahua
// Running time: 36 ms
class Solution:
  def pruneTree(self, root):
    if not root: return root
    root.left = self.pruneTree(root.left)
    root.right = self.pruneTree(root.right)
    return root if root.val == 1 or root.left or root.right else None

The post 花花酱 LeetCode 814. Binary Tree Pruning appeared first on Huahua's Tech Road.