Added countComponents solution

Author: nhistory

number-of-connected-components-in-an-undirected-graph/nhistory.js

@@ -0,0 +1,38 @@
+export class Solution {
+  /**
+   * @param n: the number of vertices
+   * @param edges: the edges of undirected graph
+   * @return: the number of connected components
+   */
+  countComponents(n, edges) {
+    // write your code here
+    const graph = Array.from({ length: n }, () => []);
+
+    for (const [node, neighbor] of edges) {
+      graph[node].push(neighbor);
+      graph[neighbor].push(node);
+    }
+
+    let visited = new Set();
+    let count = 0;
+
+    const dfs = (node) => {
+      visited.add(node);
+      for (const nei of graph[node]) {
+        if (!visited.has(nei)) dfs(nei);
+      }
+    };
+
+    for (let node = 0; node < n; node++) {
+      if (!visited.has(node)) {
+        count++;
+        dfs(node);
+      }
+    }
+    return count;
+  }
+}
+
+// n: number of node | e: number of edge
+// TC: O(n+e)
+// SC: O(n+e)