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Commit 480cdbc

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Clone Graph
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‎Graphs/133-Clone-Graph.py

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'''
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Leetcode- https://leetcode.com/problems/clone-graph/
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'''
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'''
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133. Clone Graph
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Given a reference of a node in a connected undirected graph.
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Return a deep copy (clone) of the graph.
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Each node in the graph contains a value (int) and a list (List[Node]) of its neighbors.
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class Node {
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public int val;
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public List<Node> neighbors;
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}
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Test case format:
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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.
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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.
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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.
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Example 1:
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Input: adjList = [[2,4],[1,3],[2,4],[1,3]]
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Output: [[2,4],[1,3],[2,4],[1,3]]
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Explanation: There are 4 nodes in the graph.
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1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
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2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node (val = 3).
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3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
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4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node (val = 3).
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'''
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# Definition for a Node.
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class Node:
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def __init__(self, val = 0, neighbors = None):
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self.val = val
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self.neighbors = neighbors if neighbors is not None else []
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class Solution:
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def cloneGraph(self, node: 'Node') -> 'Node':
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if not node:
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return None
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node_map = {}
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def clone(node):
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if node in node_map:
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return node_map[node]
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clone_node = Node(node.val)
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node_map[node] = clone_node
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for neighbor in node.neighbors:
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clone_node.neighbors.append(clone(neighbor))
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return clone_node
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return clone(node) if node else None
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# T: O(V + E), where V is the number of nodes and E is the number of edges in the input graph.
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'''
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Explaination of nodes:
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node1 = Node(1)
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node2 = Node(2)
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node3 = Node(3)
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node4 = Node(4)
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node1.neighbors = [node2, node4]
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node2.neighbors = [node1, node3]
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node3.neighbors = [node2, node4]
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node4.neighbors = [node1, node3]
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adjList = [node1, node2, node3, node4]
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'''
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'''
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Exlanation(solution):
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Example Graph---
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1
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/ \
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2 3
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1. The cloneGraph method is called with the node 1.
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2. node is not None, so we proceed.
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3. node_map is initialized as an empty dictionary.
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4. The clone function is defined.
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5. We enter the clone function with node as 1.
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6. node is not in node_map, so we create a clone clone_node with value 1.
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7. node_map now contains {1: clone_node}.
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8. We iterate through node.neighbors, which are 2 and 3.
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9. We recursively call clone on 2.
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10. node is not in node_map, so we create a clone clone_node with value 2.
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11. node_map now contains {1: clone_node_1, 2: clone_node_2}.
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12. We recursively call clone on 3.
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13. node is not in node_map, so we create a clone clone_node with value 3.
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14. node_map now contains {1: clone_node_1, 2: clone_node_2, 3: clone_node_3}.
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15. We finish cloning 1 and its neighbors, so we return clone_node_1 to the initial call.
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16. The cloneGraph method returns clone_node_1.
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'''

‎README.md

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- [x] [Graphs](Graphs)
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- [x] [Number of Islands](Graphs/200-Number-of-Islands.py)
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- [x] [Clone Graph](Graphs/133-Clone-Graph.py)
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