krahets/hello-algo · error · Error

Illegal Argument Exception

Error message

Illegal Argument Exception

What it means

Thrown by GraphAdjList.addEdge (TS) — the TypeScript twin of error 120 — when either endpoint Vertex is not in the adjacency list or when vet1 === vet2. TypeScript typing (Vertex) narrows the input type but does not eliminate the runtime membership/self-loop cases, so the guard remains.

Source

Thrown at ru/codes/typescript/chapter_graph/graph_adjacency_list.ts:37

            this.addVertex(edge[0]);
            this.addVertex(edge[1]);
            this.addEdge(edge[0], edge[1]);
        }
    }

    /* Получить число вершин */
    size(): number {
        return this.adjList.size;
    }

    /* Добавление ребра */
    addEdge(vet1: Vertex, vet2: Vertex): void {
        if (
            !this.adjList.has(vet1) ||
            !this.adjList.has(vet2) ||
            vet1 === vet2
        ) {
            throw new Error('Illegal Argument Exception');
        }
        // Добавить ребро vet1 - vet2
        this.adjList.get(vet1).push(vet2);
        this.adjList.get(vet2).push(vet1);
    }

    /* Удаление ребра */
    removeEdge(vet1: Vertex, vet2: Vertex): void {
        if (
            !this.adjList.has(vet1) ||
            !this.adjList.has(vet2) ||
            vet1 === vet2 ||
            this.adjList.get(vet1).indexOf(vet2) === -1
        ) {
            throw new Error('Illegal Argument Exception');
        }
        // Удалить ребро vet1 - vet2
        this.adjList.get(vet1).splice(this.adjList.get(vet1).indexOf(vet2), 1);

View on GitHub (pinned to 69932aed18)

Solutions

1. Pre-populate all vertices with addVertex before adding any edge.
2. Guard at runtime: if (g.adjList.has(v1) && g.adjList.has(v2) && v1 !== v2) g.addEdge(v1, v2).
3. Build from an edge list in two passes: vertices first, edges second.

Example fix

// before
g.addEdge(v1, v2); // throws if absent

// after
[v1, v2].forEach(v => { if (!g.adjList.has(v)) g.addVertex(v); });
if (v1 !== v2) g.addEdge(v1, v2);

function canAddEdgeTS(g, v1, v2) {
  return g.adjList.has(v1) && g.adjList.has(v2) && v1 !== v2;
}
if (canAddEdgeTS(g, v1, v2)) g.addEdge(v1, v2);

import { Vertex } from './module';
function isVertex(v: unknown): v is Vertex {
  return v != null && typeof v === 'object' && 'val' in v;
}

When it happens

Trigger: addEdge(vet1, vet2) with a Vertex not added via addVertex, or with vet1 === vet2 (same reference). TS type-checking prevents passing non-Vertex values but not absent or duplicated vertices.

Common situations: Building a graph from typed data without a first vertex-population pass; aliasing the same Vertex object for both arguments; reusing a Vertex reference after removeVertex.

Related errors

• Illegal Argument Exception
• Illegal Argument Exception
• Illegal Argument Exception
• Illegal Argument Exception
• Index Out Of Bounds Exception

AI-assisted analysis of krahets/hello-algo@69932aed18 (2026-08-13). Data as JSON: /api/errors/aea936a5c3654164. Report an issue: GitHub.