_814.java

package com.fishercoder.solutions;

import com.fishercoder.common.classes.TreeNode;

/**
 * 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.
 * 1                              1
 *  \                              \
 *   0             ---->            0
 *  / \                              \
 * 0   1                              1
 *
 *
 * Example 2:
 * Input: [1,0,1,0,0,0,1]
 * Output: [1,null,1,null,1]
 *              1                 1
 *             / \                 \
 *            0   1    ---->        1
 *           / \  / \                \
 *          0  0 0  1                1
 *
 *
 * Example 3:
 * Input: [1,1,0,1,1,0,1,0]
 * Output: [1,1,0,1,1,null,1]
 *               1                      1
 *              / \                    / \
 *             1   0     ----->       1  0
 *            / \ / \                / \  \
 *           1  1 0 1               1  1   1
 *          /
 *         0
 *
 *
 * Note:
 *
 * The binary tree will have at most 100 nodes.
 * The value of each node will only be 0 or 1.*/
public class _814 {
    public static class Solution1 {
        /**credit: https://leetcode.com/problems/binary-tree-pruning/discuss/122730/C%2B%2BJavaPython-Self-Explaining-Solution-and-2-lines*/
        public TreeNode pruneTree(TreeNode root) {
            if (root == null) {
                return root;
            }
            root.left = pruneTree(root.left);
            root.right = pruneTree(root.right);
            if (root.left == null && root.right == null && root.val == 0) {
                return null;
            }
            return root;
        }
    }
}