[LeetCode] Problem 814 - Binary Tree Pruning

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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

No.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.

EcAz1x.png

No.2

Input: [1,0,1,0,0,0,1]

Output: [1,null,1,null,1]

EcEiHe.png

No.3

Input: [1,1,0,1,1,0,1,0]

Output: [1,1,0,1,1,null,1]

EcEE4A.png

Note

  • The binary tree will have at most 100 nodes.
  • The value of each node will only be 0 or 1.

Code

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public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}
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public TreeNode pruneTree(TreeNode root) {
    if (root == null)
        return null;

    root.left = pruneTree(root.left);
    root.right = pruneTree(root.right);

    return (root.left == null && root.right == null && root.val == 0) ? null : root;
}