BinaryTreePruning.java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {

    // TC : O(n)
    // SC : O(H = logn)
    public TreeNode pruneTree(TreeNode root) {
        if (root == null) return null;
        root.left = pruneTree(root.left);
        root.right = pruneTree(root.right);

        if (canDeleteNode(root)) return null;
        return root   ;
    }

    private boolean canDeleteNode(TreeNode root){
        if(root.left == null && root.right == null && root.val == 0){
            return true;
        } else {
            return false;
        }
    }
}