1. Adjacency list
Build an empty neighbor list for every node.
const graph = Array.from({ length: n }, () => [])Typorithm · medium
Connected Components
▷ Interactive algorithm labconnected-componentsgraph-algorithmsflood-fillvisited-setcomponents
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Full lesson · 8 learning steps Open any exercise for focused practice
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Step 1 of 8 · intro card
Learn Connected Components
Graph Algorithms
Flood-fill from every unvisited node; each new flood is one connected component.
A connected component is a maximal group of nodes reachable from one another.
Scanning all nodes, each unvisited one starts a DFS that marks its whole component.
The number of times you launch a fresh DFS equals the component count.
Preparing algorithm lab…
01
Build an undirected adjacency list.
02
DFS floods one whole component.
03
Each new flood adds one to the count.
function countComponents(n, edges) {
const graph = Array.from({ length: n }, () => []);
for (const [a, b] of edges) {
graph[a].push(b);
graph[b].push(a);
}
const visited = new Set();
let count = 0;
function explore(node) {
visited.add(node);
for (const next of graph[node]) {
if (!visited.has(next)) explore(next);
}
}
for (let node = 0; node < n; node += 1) {
if (!visited.has(node)) {
count += 1;
explore(node);
}
}
return count;
}Read the implementation
Connect each part of the code to the concept before you type.
2. Both directions
An undirected edge connects both endpoints to each other.
graph[b].push(a)3. Flood a region
DFS marks every node reachable from a starting node.
function explore(node)4. New component
An unvisited node begins a brand-new component.
if (!visited.has(node))5. Count it
Each new flood is one more connected component.
count += 1A complete learning loop
01
Understand
Read the concept map and follow the code breakdown.
02
Reconstruct
Type the implementation, repair mistakes and work through every recall exercise.
03
Verify
Use the final check without hints; revisit weak concepts in short practice sessions.