#263 Number of Connected Components in an Undirected Graph

Author: forest000014

number-of-connected-components-in-an-undirected-graph/forest000014.java

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+/*
+# Time Complexity: O(n)
+# Space Comlexity: O(n + m)
+  - m = edges.length
+*/
+class Solution {
+    public int countComponents(int n, int[][] edges) {
+        ArrayList<ArrayList<Integer>> adj = new ArrayList<>();
+        for (int i = 0; i < n; i++) {
+            adj.add(new ArrayList<>());
+        }
+        for (int i = 0; i < edges.length; i++) {
+            int a = edges[i][0];
+            int b = edges[i][1];
+            adj.get(a).add(b);
+            adj.get(b).add(a);
+        }
+
+        boolean[] visited = new boolean[n];
+        int ans = 0;
+        for (int i = 0; i < n; i++) {
+            if (visited[i]) continue;
+            dfs(i, visited, adj);
+            ans++;
+        }
+
+        return ans;
+    }
+
+    public void dfs(int curr, boolean[] visited, ArrayList<ArrayList<Integer>> adj) {
+        visited[curr] = true;
+
+        for (Integer next : adj.get(curr)) {
+            if (visited[next]) continue;
+            dfs(next, visited, adj);
+        }
+    }
+}