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
