check connected components in dynamic graph

Lt547FriendCircles2.java

// 2 union find, better for checking connected components in dymanic graph
public int findCircleNum(int[][] M) {
    int[] id = new int[M.length];
    for (int i = 0; i < id.length; i++) id[i] = i;

    int[] count = new int[1];
    count[0] = id.length;
    for (int i = 0; i < M.length; i++) {
        for (int j = i; j < M[0].length; j++) {
            if (M[i][j] == 1 && i != j) union(i, j, count, id);
        }
    }

    return count[0];
}

private void union(int i, int j, int[] count, int[] id) {
    int iRoot = root(i, id);
    int jRoot = root(j, id);
    if (iRoot == jRoot) return;

    id[iRoot] = jRoot;
    count[0]--;
}

private int root(int i, int[] id) {
    while (i != id[i]) i = id[i];
    return i;
}