CSE143 4-Queens Trace               handout #21

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!