Detect Cycle in an Undirected Connected Graph (DFS)

You receive the graph as an array of edge pairs edges, where each pair [u, v] represents a bidirectional connection between nodes u and v. Implement hasCycle(edges) that:

• Builds an adjacency list from those pairs.
• Starts DFS from node 0 only.
• Returns true as soon as DFS encounters a neighbor that is visited and not the immediate parent.

Examples

Input: edges = [[0, 1], [1, 2]]
Output: false

Input: edges = [[0, 1], [1, 2], [2, 0]]
Output: true

Constraints

• Nodes are assumed to be integers that can act as object keys.
• Edges should always include the component that contains node 0; the function never explores other components.
• Inputs are expected to be well-formed arrays of two-item arrays; no explicit validation is performed.
• Self-loops or malformed inputs can lead to unexpected results because no guards are present.

Function Signature

function hasCycle(edges) {
  // Your code here
}

Test Cases

• Base cases: [], single edge [ [0, 1] ]
• Triangle: [ [4,3], [4,5], [3,5] ] -> true
• Disconnected graphs with and without cycles
• Graphs anchored at node 0 that either stay acyclic or form a cycle
• Cases where the first DFS branch already hits a back edge