Wrong Answer in FIRESC

Please help me find a wrong case for my submission http://www.codechef.com/viewsolution/3937375 .
Its giving right answers for the test cases.

Can someone explain to me what “set-union” mean with respect to this question.

That problem can be solved by union find algorithm.

The algorithm maintains tree structures (using array) which gives you the different connected components.

We maintain an array parent, such that parent[i] stores parent node of ith node, if ith node itself is independent or if ith node is a root of some connected component then parent[i] = i.

We use one more array called size, such that size[i] stores the number of all children of ith node (including ‘ith’ node)

initialize parent[i] = i for all i < vertices.size() and connected_component = 0

now algorithm iterates through all edges,

for each edge from u to v in graph G:
    u = root(u);
    v = root(v);
    if (u == v)
        already connected;
    else :
        //this condition is used to make sure that our tree doest go too deep(instead we make it
        //broad), if it goes too deep then time taken for finding root increases. 
        if (size[u] > size[v])
             parent [v] = u;
        else
             parent [u] = v;
        connected_components++;

now connected_component gives number of independent graphs in a given graph, if we want you want to find the content of independent components then run a dfs algorithm or bfs algorithm using parent array.

for more detailed explanation refer: [Alogorithms] [1]
[1]: http://algs4.cs.princeton.edu/15uf/

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