- Time limit: 1.00 s
- Memory limit: 512 MB
Uolevi's family is going to order a large pizza and eat it together. A total of n family members will join the order, and there are m possible toppings. The pizza may have any number of toppings.
Each family member gives two wishes concerning the toppings of the pizza. The wishes are of the form "topping x is good/bad". Your task is to choose the toppings so that at least one wish from everybody becomes true (a good topping is included in the pizza or a bad topping is not included).
The first input line has two integers n and m: the number of family members and toppings. The toppings are numbered 1,2,\dots,m.
After this, there are n lines describing the wishes. Each line has two wishes of the form "+ x" (topping x is good) or "- x" (topping x is bad).
Print a line with m symbols: for each topping "+" if it is included and "-" if it is not included. You can print any valid solution.
If there are no valid solutions, print "IMPOSSIBLE".
- 1 \le n,m \le 10^5
- 1 \le x \le m
3 5 + 1 + 2 - 1 + 3 + 4 - 2
- + + + -