BinaryTreePruning.java

package medium;

import util.TreeNode;

/**
 * ClassName: BinaryTreePruning.java
 * Author: chenyiAlone
 * Create Time: 2019/12/22 17:46
 * Description: No.814 Binary Tree Pruning
 *
 *
 * 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 0 or 1.
 *
 */
public class BinaryTreePruning {

    public TreeNode pruneTree(TreeNode root) {
        if (root == null) return null;
        root.left = pruneTree(root.left);
        root.right = pruneTree(root.right);
        if (root.val == 0 && root.left == null && root.right == null) return null;
        return root;
    }
    
}