- Time limit: 1.00 s
- Memory limit: 512 MB
Consider an n \times n grid whose top-left square is (1,1) and bottom-right square is (n,n).
Your task is to move from the top-left square to the bottom-right square. On each step you may move one square right or down. In addition, there are m traps in the grid. You cannot move to a square with a trap.
What is the total number of possible paths?
The first input line contains two integers n and m: the size of the grid and the number of traps.
After this, there are m lines describing the traps. Each such line contains two integers y and x: the location of a trap.
You can assume that there are no traps in the top-left and bottom-right square.
Print the number of paths modulo 10^9+7.
- 1 \le n \le 10^6
- 1 \le m \le 1000
- 1 \le y,x \le n
3 1 2 2