I hopes the following helps..

     C C C
     1 2 3
     | | |
     v v v
R1<- 1 2 3 <-pullup
R2<- 4 5 6 <-pullup
R3<- 7 8 9 <-pullup
R4<- * 0 # <-pullup

You first set C1C2C3 to 011, this means scan the C1. The read the R1R2R3R4, 0 means the button is pushed, 1 otherwise..
keep checking for 101 and 110...

Something you have to aware is that the mechanics bouncing problem. You have to do something to debounce it