✨ new: leetcode problem 814

Author: jooncco

_posts/2022-09-06-leetcode-814.md

@@ -0,0 +1,60 @@
+---
+title: "[Leetcode] 814. Binary Tree Pruning explained"
+excerpt: "Leetcode daily challenge 2022 september 6th solution"
+header:
+  overlay_image: /public/images/problem-solving-common-header.png
+tags:
+  - Tree
+  - Postorder traversal
+  - Recursion
+last_modified_at: 2022-09-06T13:11:08+09:00
+---
+
+<a href="https://leetcode.com/">
+    <img src="/public/images/leetcode-logo.jpeg"/>
+</a>
+
+## Problem
+
+<a href="https://leetcode.com/problems/binary-tree-pruning/">
+    <img src="/public/images/leetcode-814.png"/>
+</a>
+
+<br/>
+
+## Key Idea
+
+For each tree node, repeat below process.
+
+1. Prune left child.
+2. Prune right child.
+3. If left and right child is `null` and this node doesn't have value `1`, return `null` (prunning).
+
+- Time: $$O(n)$$
+- Space: $$O(n)$$
+
+<br/>
+
+## Implementation
+
+<img src="/public/images/leetcode-814-result.png"/>
+
+```java
+/**
+ * author: jooncco
+ * written: 2022. 9. 6. Tue. 13:14:14 [UTC+9]
+ **/
+
+class Solution {
+    private final int TARGET_VALUE = 1;
+
+    public TreeNode pruneTree(TreeNode root) {
+        if (root == null) return null;
+
+        root.left= pruneTree(root.left);
+        root.right= pruneTree(root.right);
+        if (root.left == null && root.right == null && root.val != TARGET_VALUE) return null;
+        return root;
+    }
+}
+```