Dominoes

practice/dominoes/dominoes.py

@@ -1,2 +1,61 @@
 def can_chain(dominoes):
-    pass
+    """
+    Determine if the given dominoes can be arranged in a chain.
+
+    This function uses a depth-first search (DFS) algorithm to try to arrange
+    the dominoes in a chain where the numbers on the ends match and each
+    domino's numbers match the numbers on the ends of the adjacent dominoes.
+
+    Args:
+        dominoes (list): A list of tuples where each tuple represents a domino
+            and contains two integers.
+
+    Returns:
+        list: A list of tuples representing the chain if one exists, or an
+            empty list if no chain exists.
+
+    Raises:
+        IndexError: An error occurs if the list is empty.
+    """
+    def dfs(chain):
+        """
+        Perform depth-first search to find a chain.
+
+        Args:
+            chain (list): The current chain of dominoes.
+
+        Returns:
+            list: A list of tuples representing the chain if one exists, or None if no chain exists.
+        """
+        # If the list of dominoes is empty, return an empty list
+        if not dominoes:
+            return []
+
+        # If all dominoes are in the chain and the chain forms a loop, return the chain
+        if len(chain) == len(dominoes) and chain and chain[0][0] == chain[-1][1]:
+            return chain
+
+        for i in range(len(dominoes)):
+            if visited[i]:
+                continue
+
+            # If the chain is empty or the last number of the last domino in the chain matches the first number of the current domino
+            if not chain or chain[-1][1] == dominoes[i][0]:
+                visited[i] = True
+                result = dfs(chain + [dominoes[i]])
+                if result:
+                    return result
+                visited[i] = False
+
+            # If the last number of the last domino in the chain matches the second number of the current domino
+            elif chain[-1][1] == dominoes[i][1]:
+                visited[i] = True
+                result = dfs(chain + [(dominoes[i][1], dominoes[i][0])])
+                if result:
+                    return result
+                visited[i] = False
+
+        return None
+
+    visited = [False] * len(dominoes)
+    return dfs([])