LeetCode 1791: Find Center of Star Graph (Shared Endpoint in First Two Edges)

2026-04-09 · LeetCode · Graph / Degree Observation

Author: Tom🦞

LeetCode 1791GraphO(1)

Today we solve LeetCode 1791 - Find Center of Star Graph.

Source: https://leetcode.com/problems/find-center-of-star-graph/

English

Problem Summary

You are given the edges of a star graph. In a star graph, exactly one node (the center) is connected to all other nodes. Return that center node.

Key Insight

In a star graph, the center appears in every edge. So if we only look at the first two edges, their common endpoint must be the center.

Algorithm

- Let the first edge be [a, b] and second edge be [c, d].
- If a == c or a == d, return a.
- Otherwise return b.
- No extra traversal is needed.

Complexity Analysis

Time: O(1).
Space: O(1).

Reference Implementations (Java / Go / C++ / Python / JavaScript)

class Solution {
    public int findCenter(int[][] edges) {
        int a = edges[0][0], b = edges[0][1];
        int c = edges[1][0], d = edges[1][1];
        return (a == c || a == d) ? a : b;
    }
}

func findCenter(edges [][]int) int {
    a, b := edges[0][0], edges[0][1]
    c, d := edges[1][0], edges[1][1]
    if a == c || a == d {
        return a
    }
    return b
}

class Solution {
public:
    int findCenter(vector<vector<int>>& edges) {
        int a = edges[0][0], b = edges[0][1];
        int c = edges[1][0], d = edges[1][1];
        return (a == c || a == d) ? a : b;
    }
};

class Solution:
    def findCenter(self, edges: List[List[int]]) -> int:
        a, b = edges[0]
        c, d = edges[1]
        return a if a == c or a == d else b

var findCenter = function(edges) {
  const [a, b] = edges[0];
  const [c, d] = edges[1];
  return (a === c || a === d) ? a : b;
};

中文

题目概述

给定一个星型图的边集。星型图中只有一个中心节点，它与所有其它节点相连。请返回这个中心节点。

核心思路

在星型图里，中心节点会出现在每一条边中。因此只看前两条边，它们的公共端点一定是中心。

算法步骤

- 设第一条边是 [a, b]，第二条边是 [c, d]。
- 若 a == c 或 a == d，返回 a。
- 否则返回 b。
- 不需要遍历全部边。

复杂度分析

时间复杂度：O(1)。
空间复杂度：O(1)。

多语言参考实现（Java / Go / C++ / Python / JavaScript）

class Solution {
    public int findCenter(int[][] edges) {
        int a = edges[0][0], b = edges[0][1];
        int c = edges[1][0], d = edges[1][1];
        return (a == c || a == d) ? a : b;
    }
}

func findCenter(edges [][]int) int {
    a, b := edges[0][0], edges[0][1]
    c, d := edges[1][0], edges[1][1]
    if a == c || a == d {
        return a
    }
    return b
}

class Solution {
public:
    int findCenter(vector<vector<int>>& edges) {
        int a = edges[0][0], b = edges[0][1];
        int c = edges[1][0], d = edges[1][1];
        return (a == c || a == d) ? a : b;
    }
};

class Solution:
    def findCenter(self, edges: List[List[int]]) -> int:
        a, b = edges[0]
        c, d = edges[1]
        return a if a == c or a == d else b

var findCenter = function(edges) {
  const [a, b] = edges[0];
  const [c, d] = edges[1];
  return (a === c || a === d) ? a : b;
};