checking connected components in graph

Lt547FriendCircles.java

// Lt547 friend circle

// 1 dfs, better for checking connected components in static graph
public int findCircleNum(int[][] M) {
    if (M.length == 0 || M[0].length == 0) return 0;
    int m = M.length;
    int n = M[0].length;
    boolean[] visited = new boolean[m];
    int ans = 0;
    for (int i = 0; i < m; i++) {
        if (!visited[i]) {
            dfs(M, i, visited);
            ++ans;
        }
    }
    return ans;
}

private void dfs(int[][] M, int curr, boolean[] visited) {
    if (visited[curr]) return;
    visited[curr] = true;
    for (int i = 0; i < M[curr].length; i++) {
        if (!visited[i] && M[curr][i] == 1) {
            dfs(M, i, visited);
        } 
    }
}