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1791. Find Center of Star Graph

Difficulty Topics

Description

There is an undirected star graph consisting of n nodes labeled from 1 to n. A star graph is a graph where there is one center node and exactly n - 1 edges that connect the center node with every other node.

You are given a 2D integer array edges where each edges[i] = [ui, vi] indicates that there is an edge between the nodes ui and vi. Return the center of the given star graph.

 

Example 1:

Input: edges = [[1,2],[2,3],[4,2]]
Output: 2
Explanation: As shown in the figure above, node 2 is connected to every other node, so 2 is the center.

Example 2:

Input: edges = [[1,2],[5,1],[1,3],[1,4]]
Output: 1

 

Constraints:

  • 3 <= n <= 105
  • edges.length == n - 1
  • edges[i].length == 2
  • 1 <= ui, vi <= n
  • ui != vi
  • The given edges represent a valid star graph.

Solution

find-center-of-star-graph.py
class Solution:
    def findCenter(self, edges: List[List[int]]) -> int:
        n = len(edges)
        mp = collections.defaultdict(int)

        for a,b in edges:
            mp[a] += 1
            mp[b] += 1

        for key in mp:
            if mp[key] == n:
                return key

        return -1