CSE143
4-Queens Trace               handout
#25
explore col 1
        1--place, explore col 2
                1
                2
                3--place,
explore col 3
                        1
                        2
                        3
                        4
                4--place,
explore col 3
                        1
                       
2--place, explore col 4
                               
1
                               
2
                               
3
                               
4
                        3
                        4
        2--place, explore col 2
                1
                2
                3
                4--place,
explore col 3
                       
1--place, explore col 4
                              
 1
                               
2
                               
3--place, explore col 5
                                        done!
