case 2 failed: runtime error: exit status 2
panic: runtime error: index out of range [-1]

goroutine 1 [running]:
main.main.func1()
	/tmp/build-155798199/solution.go:158 +0x2d0
main.main()
	/tmp/build-155798199/solution.go:162 +0x2dc

input:
8 3
bwwbbbbb
2 b
4 b
7 w
exit status 1