I am getting wrong answer (on test 15) for this problem : 687A - NP-Hard Problem

Here is my code : 51436363

Solution description : I have used concept of bipartitie graphs. If the graph is a bipartitie graph then solution is possible otherwise not. I have made a vector "dist" in which i have stored the distance of vertices from the source vertex. All the vertices at "odd" distance from the source go to vector "v2" and those with "even" distance go to vector "v1".

I have just started to learn graph theory so please tell me what is wrong with the logic and code.