BFS vs DFS

Breadth-first search and depth-first search can both visit every reachable node.

Breadth-First Search

BFS explores level by level using a queue.

const queue = [start];
const seen = new Set([start]);

while (queue.length) {
  const node = queue.shift()!;

  for (const next of graph[node]) {
    if (seen.has(next)) continue;

    seen.add(next);
    queue.push(next);
  }
}

Depth-First Search

function dfs(node: number) {
  seen.add(node);

  for (const next of graph[node]) {
    if (!seen.has(next)) {
      dfs(next);
    }
  }
}

With an adjacency list, both typically run in O(V + E).

Use BFS when levels or shortest unweighted distance matter. Use DFS when deep recursive exploration fits naturally.