Rikka with wood sticks
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/65536 K (Java/Others)
Total Submission(s): 1166 Accepted Submission(s): 356
we know, Rikka is poor at math. Yuta is worrying about this situation,
so he gives Rikka some math tasks to practice. There is one of them:
Yuta have a wood stick of length n which consists of n linked sticks of length 1. So it has n−1 connection points. Yuta finds that some sticks of length 1
of the wood stick are not strong. So he wants to choose three different
connection points to cut it into four wood sticks and only one of them
contains wood sticks which are not strong. And Yuta wants to minimize
the length of this piece which contains bad wood sticks. Besides, Rikka
wants to use the other three wood sticks to make a triangle. Now she
wants to count the number of the ways to cut the wood sticks which can
make both Yuta and herself happy.
It is too difficult for Rikka. Can you help her?
This problem has multi test cases (no more than 20). For each test case, The first line contains two numbers n,m(1≤n≤1000000,1≤m≤1000). The next line contains m numbers (some of them may be same) – the position of each wood sticks which is not strong.
For each test cases print only one number – the ways to cut the wood sticks.