TheAlgorithms/Java · error · IllegalArgumentException

Edge vertex out of range

Error message

Edge vertex out of range

What it means

Thrown by `checkEdgeVertices` during Graph construction when any edge's `src` or `dest` is negative or `>= vertex`. Every edge endpoint must index a real vertex in `[0, vertex)`. This catches malformed or off-by-one edge definitions before they corrupt the MST computation.

Source

Thrown at src/main/java/com/thealgorithms/datastructures/graphs/BoruvkaAlgorithm.java:214

    static List<Edge> boruvkaMST(final Graph graph) {
        var boruvkaState = new BoruvkaState(graph);

        while (boruvkaState.hasMoreEdgesToAdd()) {
            final var cheapest = boruvkaState.computeCheapestEdges();
            boruvkaState.merge(cheapest);
        }
        return boruvkaState.result;
    }

    /**
     * Checks if the edge vertices are in a valid range
     *
     * @param vertex     the vertex to check
     * @param upperBound the upper bound for the vertex range
     */
    private static void checkEdgeVertices(final int vertex, final int upperBound) {
        if (vertex < 0 || vertex >= upperBound) {
            throw new IllegalArgumentException("Edge vertex out of range");
        }
    }
}

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Make vertex indices 0-based and ensure all src/dest are in [0, vertex)
2. If your data is 1-based, subtract 1 from every endpoint before building Edges
3. Set `vertex` to at least `max(src,dest)+1` across all edges

Example fix

// before (1-based data passed directly)
edges.add(new Edge(1, vertex, w));
// after (convert 1-based to 0-based)
edges.add(new Edge(src - 1, dest - 1, w));

for (Edge e : edges) {
    if (e.src < 0 || e.src >= vertex || e.dest < 0 || e.dest >= vertex) {
        throw new IllegalArgumentException("bad edge " + e.src + "-" + e.dest);
    }
}

try {
    new BoruvkaAlgorithm.Graph(v, edges);
} catch (IllegalArgumentException e) {
    // log the offending edge
}

When it happens

Trigger: An Edge whose `src`/`dest` equals `vertex` (1-based index passed to a 0-based graph), is negative, or references a vertex that does not exist because the vertex count was set too low.

Common situations: Mixing 1-based file data with the 0-based API; vertex count smaller than the max referenced vertex; an edge list built for a larger graph but a smaller `vertex` passed.

Related errors

• Source vertex is out of bounds.
• Vertex {vertex} is out of bounds
• Number of vertices must be positive
• Edges list must not be null or empty
• Incorrect source

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/9798d55ce489d86b. Report an issue: GitHub.