547_Friend_Circles.java

public class Solution {
    public void dfs(int[][] M, int[] visited, int i) {
        for (int j = 0; j < M.length; j++) {
            if (M[i][j] == 1 && visited[j] == 0) {
                visited[j] = 1;
                dfs(M, visited, j);
            }
        }
    }
    public int findCircleNum(int[][] M) {
        // DFS
        int[] visited = new int[M.length];
        int count = 0;
        for (int i = 0; i < M.length; i++) {
            if (visited[i] == 0) {
                dfs(M, visited, i);
                count++;
            }
        }
        return count;
    }

    /*public int findCircleNum(int[][] M) {
        // BFS
        int[] visited = new int[M.length];
        int count = 0;
        Queue < Integer > queue = new LinkedList < > ();
        for (int i = 0; i < M.length; i++) {
            if (visited[i] == 0) {
                queue.add(i);
                while (!queue.isEmpty()) {
                    int s = queue.remove();
                    visited[s] = 1;
                    for (int j = 0; j < M.length; j++) {
                        if (M[s][j] == 1 && visited[j] == 0)
                            queue.add(j);
                    }
                }
                count++;
            }
        }
        return count;
    }*/

    /*
    // Union find
    int find(int parent[], int i) {
        if (parent[i] == -1)
            return i;
        return find(parent, parent[i]);
    }

    void union(int parent[], int x, int y) {
        int xset = find(parent, x);
        int yset = find(parent, y);
        if (xset != yset)
            parent[xset] = yset;
    }
    public int findCircleNum(int[][] M) {
        int[] parent = new int[M.length];
        Arrays.fill(parent, -1);
        for (int i = 0; i < M.length; i++) {
            for (int j = 0; j < M.length; j++) {
                if (M[i][j] == 1 && i != j) {
                    union(parent, i, j);
                }
            }
        }
        int count = 0;
        for (int i = 0; i < parent.length; i++) {
            if (parent[i] == -1)
                count++;
        }
        return count;
    }*/
}