Can we use dijkstra algorithm to find maximum bipartite matching with minimum cost? If we can,how??

How can we find Independent set such that the sum of weight is maximum; We should not maximize the number of node;

https://ideone.com/uO7jxh

How can we efficeiently find MEX(minimum excluded) of an array?

What is the maximum array size we can declare in codeforces for long long data types? thanks in advance