Nov 30

Author: siddydutta

2024-11-November-LeetCoding-Challenge/README.md

@@ -32,11 +32,11 @@
 | November 27 | [3243. Shortest Distance After Road Addition Queries I](https://leetcode.com/problems/shortest-distance-after-road-addition-queries-i/) | Medium | Solved |
 | November 28 | [2290. Minimum Obstacle Removal to Reach Corner](https://leetcode.com/problems/minimum-obstacle-removal-to-reach-corner/) | Hard | Unsolved |
 | November 29 | [2577. Minimum Time to Visit a Cell In a Grid](https://leetcode.com/problems/minimum-time-to-visit-a-cell-in-a-grid/) | Hard | Unsolved |
-| November 30 | []() |  |  |
+| November 30 | [2097. Valid Arrangement of Pairs](https://leetcode.com/problems/valid-arrangement-of-pairs/) | Hard | Unsolved |
 
 ## Summary
 | Level  | Problems | Solved | Unsolved |
 | ---    | --- | --- | --- |
 | Easy   | 4 | 4 | 0 |
 | Medium | 21 | 12 | 9 |
-| Hard   | 4 | 1 | 3 |
+| Hard   | 5 | 1 | 4 |

2024-11-November-LeetCoding-Challenge/Valid Arrangement of Pairs.py

@@ -0,0 +1,48 @@
+from collections import defaultdict
+from typing import List
+
+
+class Solution:
+    def validArrangement(self, pairs: List[List[int]]) -> List[List[int]]:
+        graph = defaultdict(list)
+        in_degree, out_degree = defaultdict(int), defaultdict(int)
+        for u, v in pairs:
+            graph[u].append(v)
+            out_degree[u] += 1
+            in_degree[v] += 1
+
+        start = pairs[0][0]
+        for node in graph:
+            if out_degree[node] > in_degree[node]:
+                start = node
+                break
+
+        result = []
+        stack = [start]
+        while stack:
+            node = stack[-1]
+            if graph[node]:
+                neighbour = graph[node].pop()
+                stack.append(neighbour)
+            else:
+                stack.pop()
+                if stack:
+                    result.append([stack[-1], node])
+        result.reverse()
+        return result
+
+
+def main():
+    pairs = [[5, 1], [4, 5], [11, 9], [9, 4]]
+    assert Solution().validArrangement(pairs) == [[11, 9], [9, 4],
+                                                  [4, 5], [5, 1]]
+
+    pairs = [[1, 3], [3, 2], [2, 1]]
+    assert Solution().validArrangement(pairs) == [[1, 3], [3, 2], [2, 1]]
+
+    pairs = [[1, 2], [1, 3], [2, 1]]
+    assert Solution().validArrangement(pairs) == [[1, 2], [2, 1], [1, 3]]
+
+
+if __name__ == '__main__':
+    main()