Test the splitMap
s1: size =2   0 1 4  | 2 3 
s2: size =2   0 2 3  | 1 4 

add s1
1	size =2   0 1 4  | 2 3 

add s2
1	size =2   0 1 4  | 2 3 
1	size =2   0 2 3  | 1 4 

add s1
2	size =2   0 1 4  | 2 3 
1	size =2   0 2 3  | 1 4 

add s1
3	size =2   0 1 4  | 2 3 
1	size =2   0 2 3  | 1 4 

add s1
4	size =2   0 1 4  | 2 3 
1	size =2   0 2 3  | 1 4 


print test
4	size =2   0 1 4  | 2 3 
1	size =2   0 2 3  | 1 4 


reverse the map
4 size =2   0 1 4  | 2 3 

1 size =2   0 2 3  | 1 4