Fix mypy errors at kruskal_2 (#4528)

graphs/minimum_spanning_tree_kruskal2.py

@@ -1,78 +1,93 @@
 from __future__ import annotations
 
+from typing import Generic, TypeVar
 
-class DisjointSetTreeNode:
+T = TypeVar("T")
+
+
+class DisjointSetTreeNode(Generic[T]):
     # Disjoint Set Node to store the parent and rank
-    def __init__(self, key: int) -> None:
+    def __init__(self, data: T) -> None:
-        self.key = key
+        self.data = data
         self.parent = self
         self.rank = 0
 
 
-class DisjointSetTree:
+class DisjointSetTree(Generic[T]):
     # Disjoint Set DataStructure
-    def __init__(self):
+    def __init__(self) -> None:
         # map from node name to the node object
-        self.map = {}
+        self.map: dict[T, DisjointSetTreeNode[T]] = {}
 
-    def make_set(self, x: int) -> None:
+    def make_set(self, data: T) -> None:
         # create a new set with x as its member
-        self.map[x] = DisjointSetTreeNode(x)
+        self.map[data] = DisjointSetTreeNode(data)
 
-    def find_set(self, x: int) -> DisjointSetTreeNode:
+    def find_set(self, data: T) -> DisjointSetTreeNode[T]:
         # find the set x belongs to (with path-compression)
-        elem_ref = self.map[x]
+        elem_ref = self.map[data]
         if elem_ref != elem_ref.parent:
-            elem_ref.parent = self.find_set(elem_ref.parent.key)
+            elem_ref.parent = self.find_set(elem_ref.parent.data)
         return elem_ref.parent
 
-    def link(self, x: int, y: int) -> None:
+    def link(
+        self, node1: DisjointSetTreeNode[T], node2: DisjointSetTreeNode[T]
+    ) -> None:
         # helper function for union operation
-        if x.rank > y.rank:
+        if node1.rank > node2.rank:
-            y.parent = x
+            node2.parent = node1
         else:
-            x.parent = y
+            node1.parent = node2
-            if x.rank == y.rank:
+            if node1.rank == node2.rank:
-                y.rank += 1
+                node2.rank += 1
 
-    def union(self, x: int, y: int) -> None:
+    def union(self, data1: T, data2: T) -> None:
         # merge 2 disjoint sets
-        self.link(self.find_set(x), self.find_set(y))
+        self.link(self.find_set(data1), self.find_set(data2))
 
 
-class GraphUndirectedWeighted:
+class GraphUndirectedWeighted(Generic[T]):
-    def __init__(self):
+    def __init__(self) -> None:
         # connections: map from the node to the neighbouring nodes (with weights)
-        self.connections = {}
+        self.connections: dict[T, dict[T, int]] = {}
 
-    def add_node(self, node: int) -> None:
+    def add_node(self, node: T) -> None:
         # add a node ONLY if its not present in the graph
         if node not in self.connections:
             self.connections[node] = {}
 
-    def add_edge(self, node1: int, node2: int, weight: int) -> None:
+    def add_edge(self, node1: T, node2: T, weight: int) -> None:
         # add an edge with the given weight
         self.add_node(node1)
         self.add_node(node2)
         self.connections[node1][node2] = weight
         self.connections[node2][node1] = weight
 
-    def kruskal(self) -> GraphUndirectedWeighted:
+    def kruskal(self) -> GraphUndirectedWeighted[T]:
         # Kruskal's Algorithm to generate a Minimum Spanning Tree (MST) of a graph
         """
         Details: https://en.wikipedia.org/wiki/Kruskal%27s_algorithm
 
         Example:
-
+        >>> g1 = GraphUndirectedWeighted[int]()
-        >>> graph = GraphUndirectedWeighted()
+        >>> g1.add_edge(1, 2, 1)
-        >>> graph.add_edge(1, 2, 1)
+        >>> g1.add_edge(2, 3, 2)
-        >>> graph.add_edge(2, 3, 2)
+        >>> g1.add_edge(3, 4, 1)
-        >>> graph.add_edge(3, 4, 1)
+        >>> g1.add_edge(3, 5, 100) # Removed in MST
-        >>> graph.add_edge(3, 5, 100) # Removed in MST
+        >>> g1.add_edge(4, 5, 5)
-        >>> graph.add_edge(4, 5, 5)
+        >>> assert 5 in g1.connections[3]
-        >>> assert 5 in graph.connections[3]
+        >>> mst = g1.kruskal()
-        >>> mst = graph.kruskal()
         >>> assert 5 not in mst.connections[3]
+
+        >>> g2 = GraphUndirectedWeighted[str]()
+        >>> g2.add_edge('A', 'B', 1)
+        >>> g2.add_edge('B', 'C', 2)
+        >>> g2.add_edge('C', 'D', 1)
+        >>> g2.add_edge('C', 'E', 100) # Removed in MST
+        >>> g2.add_edge('D', 'E', 5)
+        >>> assert 'E' in g2.connections["C"]
+        >>> mst = g2.kruskal()
+        >>> assert 'E' not in mst.connections['C']
         """
 
         # getting the edges in ascending order of weights
@@ -84,26 +99,23 @@ class GraphUndirectedWeighted:
                     seen.add((end, start))
                     edges.append((start, end, self.connections[start][end]))
         edges.sort(key=lambda x: x[2])
+
         # creating the disjoint set
-        disjoint_set = DisjointSetTree()
+        disjoint_set = DisjointSetTree[T]()
-        [disjoint_set.make_set(node) for node in self.connections]
+        for node in self.connections:
+            disjoint_set.make_set(node)
+
         # MST generation
         num_edges = 0
         index = 0
-        graph = GraphUndirectedWeighted()
+        graph = GraphUndirectedWeighted[T]()
         while num_edges < len(self.connections) - 1:
             u, v, w = edges[index]
             index += 1
-            parentu = disjoint_set.find_set(u)
+            parent_u = disjoint_set.find_set(u)
-            parentv = disjoint_set.find_set(v)
+            parent_v = disjoint_set.find_set(v)
-            if parentu != parentv:
+            if parent_u != parent_v:
                 num_edges += 1
                 graph.add_edge(u, v, w)
                 disjoint_set.union(u, v)
         return graph
-
-
-if __name__ == "__main__":
-    import doctest
-
-    doctest.testmod()