Merge pull request #1539 from YoungSeok-Choi/feature/week-10

[YoungSeok-Choi] Week 10 Solutions

Author: TonyKim9401

invert-binary-tree/YoungSeok-Choi.java

@@ -0,0 +1,71 @@
+import java.util.HashMap;
+import java.util.Map;
+
+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;
+    }
+}
+
+// tc -> O(n)
+class Solution {
+
+    public TreeNode invertTree(TreeNode root) {
+        if (root == null)
+            return null;
+
+        TreeNode left = invertTree(root.left);
+        TreeNode right = invertTree(root.right);
+
+        root.right = left;
+        root.left = right;
+
+        return root;
+    }
+
+}
+
+// NOTE: deep copy 작업도 해볼 것
+// 같은 val의 Node가 여러 개 들어오는 경우를 고려하지 못했음..
+class WrongSolution {
+
+    public Map<Integer, TreeNode> tMap = new HashMap<>();
+
+    public TreeNode invertTree(TreeNode root) {
+        if (root == null)
+            return null;
+
+        int rVal = root.val;
+
+        tMap.computeIfAbsent(rVal, k -> new TreeNode(k));
+
+        TreeNode cur = tMap.get(rVal);
+
+        if (root.left != null) {
+            tMap.computeIfAbsent(root.left.val, k -> new TreeNode(k));
+            cur.right = tMap.get(root.left.val);
+            invertTree(root.left);
+        }
+
+        if (root.right != null) {
+            tMap.computeIfAbsent(root.right.val, k -> new TreeNode(k));
+            cur.left = tMap.get(root.right.val);
+            invertTree(root.right);
+        }
+
+        return tMap.get(root.val);
+    }
+}