1325.delete-leaves-with-a-given-value.java

/*
 * @lc app=leetcode id=1325 lang=java
 *
 * [1325] Delete Leaves With a Given Value
 *
 * https://leetcode.com/problems/delete-leaves-with-a-given-value/description/
 *
 * algorithms
 * Medium (72.82%)
 * Likes:    227
 * Dislikes: 4
 * Total Accepted:    14.8K
 * Total Submissions: 20.4K
 * Testcase Example:  '[1,2,3,2,null,2,4]\n2'
 *
 * Given a binary tree root and an integer target, delete all the leaf nodes
 * with value target.
 * 
 * Note that once you delete a leaf node with value target, if it's parent node
 * becomes a leaf node and has the value target, it should also be deleted (you
 * need to continue doing that until you can't).
 * 
 * 
 * Example 1:
 * 
 * 
 * 
 * 
 * Input: root = [1,2,3,2,null,2,4], target = 2
 * Output: [1,null,3,null,4]
 * Explanation: Leaf nodes in green with value (target = 2) are removed
 * (Picture in left). 
 * After removing, new nodes become leaf nodes with value (target = 2) (Picture
 * in center).
 * 
 * 
 * Example 2:
 * 
 * 
 * 
 * 
 * Input: root = [1,3,3,3,2], target = 3
 * Output: [1,3,null,null,2]
 * 
 * 
 * Example 3:
 * 
 * 
 * 
 * 
 * Input: root = [1,2,null,2,null,2], target = 2
 * Output: [1]
 * Explanation: Leaf nodes in green with value (target = 2) are removed at each
 * step.
 * 
 * 
 * Example 4:
 * 
 * 
 * Input: root = [1,1,1], target = 1
 * Output: []
 * 
 * 
 * Example 5:
 * 
 * 
 * Input: root = [1,2,3], target = 1
 * Output: [1,2,3]
 * 
 * 
 * 
 * Constraints:
 * 
 * 
 * 1 <= target <= 1000
 * Each tree has at most 3000 nodes.
 * Each node's value is between [1, 1000].
 * 
 */

// @lc code=start
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode removeLeafNodes(TreeNode root, int target) {
        if (root == null) return root;

        root.left = removeLeafNodes(root.left, target);
        root.right = removeLeafNodes(root.right, target);

        if (root.left == null && root.right == null && root.val == target) {
            return null;
        } else {
            return root;
        }
    }
}
// @lc code=end