814. Binary Tree Pruning

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814. Binary Tree Pruning

Description

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:

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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:

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

Example 3:

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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.

Hints/Notes

  • binary tree
  • No solution from 0x3F

Solution

Language: C++

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left),
 * right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* pruneTree(TreeNode* root) {
        if (!root) {
            return root;
        }
        root->left = pruneTree(root->left);
        root->right = pruneTree(root->right);

        if (!root->left && !root->right && root->val == 0) {
            return nullptr;
        }
        return root;
    }
};