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0951-flip-equivalent-binary-trees/0951-flip-equivalent-binary-trees.java

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+/**
+ * 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 {
+    public boolean flipEquiv(TreeNode root1, TreeNode root2) {
+        if (root1 == null && root2 == null) return true;
+        if (root1 == null || root2 == null || root1.val != root2.val) return false;
+
+        Set<List<Integer>> set = new HashSet<>();
+        Set<List<Integer>> visited = new HashSet<>();
+
+        getPath(root1, new ArrayList<>(), set);
+
+        if (!checkPath(root2, new ArrayList<>(), set, visited)) {
+            return false;
+        }
+
+        return set.equals(visited);
+    }
+
+    private void getPath(TreeNode node, List<Integer> currPath, Set<List<Integer>> paths) {
+        if (node == null) return;
+
+        currPath.add(node.val);
+
+        if (node.left == null && node.right == null) {
+            paths.add(new ArrayList<>(currPath));
+        } else {
+            getPath(node.left, currPath, paths);
+            getPath(node.right, currPath, paths);
+        }
+
+        currPath.remove(currPath.size() - 1);
+    }
+
+    private boolean checkPath(TreeNode node, List<Integer> currPath, Set<List<Integer>> set, Set<List<Integer>> visited) {
+        if (node == null) return true;
+
+        currPath.add(node.val);
+
+        if (node.left == null && node.right == null) {
+            List<Integer> path = new ArrayList<>(currPath);
+            if (!set.contains(path)) return false;
+            visited.add(path);
+        } 
+        else {
+            boolean left = checkPath(node.left, currPath, set, visited);
+            boolean right = checkPath(node.right, currPath, set, visited);
+            if (!left || !right) return false;
+        }
+
+        currPath.remove(currPath.size() - 1);
+        return true;
+    }
+}