Update README.md

solution/2000-2099/2097.Valid Arrangement of Pairs/README.md

@@ -89,6 +89,32 @@ end<sub>1</sub> = 1 == 1 = start<sub>2</sub>
 #### Python3
 
 ```python
+class Solution:
+    def validArrangement(self, pairs):
+        graph = defaultdict(deque)
+        degree = defaultdict(int)
+
+        for u, v in pairs:
+            graph[u].append(v)
+            degree[u] += 1
+            degree[v] -= 1
+
+        start = pairs[0][0]
+        for node in graph:
+            if degree[node] > 0:
+                start = node
+                break
+
+        path = []
+
+        def traverse(node):
+            while graph[node]:
+                traverse(graph[node].popleft())
+            path.append(node)
+
+        traverse(start)
+        path.reverse()
+        return [[path[i], path[i + 1]] for i in range(len(path) - 1)]
 
 ```