feat(work): add solutions for number-of-islands, pacific-atlantic-water-flow, and clone-graph problems

work/1/Medium/Hash Table/133.clone-graph.py

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+"""
+133. Clone Graph
+Difficulty: Medium
+https://leetcode.com/problems/clone-graph/
+
+──────────────────────────────────────────────────
+
+Given a reference of a node in a connected undirected graph.
+
+Return a deep copy (clone) of the graph.
+
+Each node in the graph contains a value (int) and a list (List[Node])
+of its neighbors.
+
+class Node {
+    public int val;
+    public List<Node> neighbors;
+}
+
+
+
+Test case format:
+
+For simplicity, each node's value is the same as the node's index
+(1-indexed). For example, the first node with val == 1, the second
+node with val == 2, and so on. The graph is represented in the test
+case using an adjacency list.
+
+An adjacency list is a collection of unordered lists used to
+represent a finite graph. Each list describes the set of neighbors of
+a node in the graph.
+
+The given node will always be the first node with val = 1. You must
+return the copy of the given node as a reference to the cloned graph.
+
+
+
+Example 1:
+
+Input: adjList = [[2,4],[1,3],[2,4],[1,3]]
+Output: [[2,4],[1,3],[2,4],[1,3]]
+Explanation: There are 4 nodes in the graph.
+1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node
+(val = 4).
+2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node
+(val = 3).
+3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node
+(val = 4).
+4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node
+(val = 3).
+
+Example 2:
+
+Input: adjList = [[]]
+Output: [[]]
+Explanation: Note that the input contains one empty list. The graph
+consists of only one node with val = 1 and it does not have any
+neighbors.
+
+Example 3:
+
+Input: adjList = []
+Output: []
+Explanation: This an empty graph, it does not have any nodes.
+
+
+
+Constraints:
+
+        • The number of nodes in the graph is in the range [0, 100].
+
+        • 1 <= Node.val <= 100
+
+        • Node.val is unique for each node.
+
+        • There are no repeated edges and no self-loops in the graph.
+
+• The Graph is connected and all nodes can be visited starting from
+the given node.
+"""
+
+"""
+# Definition for a Node.
+class Node:
+    def __init__(self, val = 0, neighbors = None):
+        self.val = val
+        self.neighbors = neighbors if neighbors is not None else []
+"""
+
+from typing import Optional
+
+
+class Solution:
+    def cloneGraph(self, node: Optional["Node"]) -> Optional["Node"]:
+        oldToNew = {}
+
+        def dfs(node):
+            if node in oldToNew:
+                return oldToNew[node]
+
+            copy = Node(node.val)
+            oldToNew[node] = copy
+
+            for n in node.neighbors:
+                copy.neighbors.append(dfs(n))
+            return copy
+
+        return dfs(node) if node else None