void make_set(int v) {
    parent[v] = v;
}

int find_set(int v) {
    if (v == parent[v])
        return v;
    return find_set(parent[v]);
}

void union_sets(int a, int b) {
    a = find_set(a);
    b = find_set(b);
    if (a != b)
        parent[b] = a;
}

is a naive implementation of disjoint set union algorithm, according to a article now i don't understand that if parent[3] = 1 and parent[2] = 1 and parent[1] = 1 after using union_sets(1, 2); union_sets(2, 3); but on the visual represntaiton of the set 3 should be the child of 2 but parent[3] is 1.