描述
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
Note:
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.
解析
根据题意，肯定有一个中心点，而且有 n-1 条边，由于各种附属条件限制，只需要找到在 edges 中至少出现两次的点即可，所以遍历 edges ，对其中的点进行计数，只要有出现两次的点即为中心点。
解答
class Solution(object):
def findCenter(self, edges):
"""
:type edges: List[List[int]]
:rtype: int
"""
d = {}
n = len(edges)
for edge in edges:
if edge[0] not in d:
d[edge[0]] = 1
else:
d[edge[0]] += 1
if d[edge[0]] == 2:
return edge[0]
if edge[1] not in d:
d[edge[1]] = 1
else:
d[edge[1]] += 1
if d[edge[1]] == 2:
return edge[1]
return -1
运行结果
Runtime: 684 ms, faster than 100.00% of Python online submissions for Find Center of Star Graph.
Memory Usage: 52.5 MB, less than 100.00% of Python online submissions for Find Center of Star Graph.
原题链接：https://leetcode.com/problems/find-center-of-star-graph/
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