[subject line]
add find median/Kth element of sorted two arrays
add plus one
[Bug input/output]

[Fix]
add first impl of plus one
[Bug input/output]

[Fix]
[subject line]
add four sum problem
[Bug input/output]
input   output  expected
[-3,-2,-1,0,0,1,2,3], 0
[[-3,-2,2,3],[-3,-1,1,3],[-3,0,0,3],[-3,0,1,2],[-3,0,1,2],[-2,-1,0,3],[-2,-1,0,3],[-2,-1,1,2],[-2,0,0,2],[-1,0,0,1]]
[[-3,-2,2,3],[-3,-1,1,3],[-3,0,0,3],[-3,0,1,2],[-2,-1,0,3],[-2,-1,1,2],[-2,0,0,2],[-1,0,0,1]]

[Fix]
see next commit
[subject line]
add 4 sum fix
[Bug input/output]

[Fix]