[+] placed queen at (0,0) [>] CALL solve(1) [x] can't place queen at (1,0) [x] can't place queen at (1,1) [+] placed queen at (1,2) [>] CALL solve(2) [x] can't place queen at (2,0) [x] can't place queen at (2,1) [x] can't place queen at (2,2) [x] can't place queen at (2,3) [-] removed queen at (1,2) [+] placed queen at (1,3) [>] CALL solve(2) [x] can't place queen at (2,0) [+] placed queen at (2,1) [>] CALL solve(3) [x] can't place queen at (3,0) [x] can't place queen at (3,1) [x] can't place queen at (3,2) [x] can't place queen at (3,3) [-] removed queen at (2,1) [x] can't place queen at (2,2) [x] can't place queen at (2,3) [-] removed queen at (1,3) [-] removed queen at (0,0) [+] placed queen at (0,1) [>] CALL solve(1) [x] can't place queen at (1,0) [x] can't place queen at (1,1) [x] can't place queen at (1,2) [+] placed queen at (1,3) [>] CALL solve(2) [+] placed queen at (2,0) [>] CALL solve(3) [x] can't place queen at (3,0) [x] can't place queen at (3,1) [+] placed queen at (3,2) [>] CALL solve(4) [*] SUCCESS solution = { 1 3 0 2} [-] removed queen at (3,2) [x] can't place queen at (3,3) [-] removed queen at (2,0) [x] can't place queen at (2,1) [x] can't place queen at (2,2) [x] can't place queen at (2,3) [-] removed queen at (1,3) [-] removed queen at (0,1) [+] placed queen at (0,2) [>] CALL solve(1) [+] placed queen at (1,0) [>] CALL solve(2) [x] can't place queen at (2,0) [x] can't place queen at (2,1) [x] can't place queen at (2,2) [+] placed queen at (2,3) [>] CALL solve(3) [x] can't place queen at (3,0) [+] placed queen at (3,1) [>] CALL solve(4) [*] SUCCESS solution = { 2 0 3 1} [-] removed queen at (3,1) [x] can't place queen at (3,2) [x] can't place queen at (3,3) [-] removed queen at (2,3) [-] removed queen at (1,0) [x] can't place queen at (1,1) [x] can't place queen at (1,2) [x] can't place queen at (1,3) [-] removed queen at (0,2) [+] placed queen at (0,3) [>] CALL solve(1) [+] placed queen at (1,0) [>] CALL solve(2) [x] can't place queen at (2,0) [x] can't place queen at (2,1) [+] placed queen at (2,2) [>] CALL solve(3) [x] can't place queen at (3,0) [x] can't place queen at (3,1) [x] can't place queen at (3,2) [x] can't place queen at (3,3) [-] removed queen at (2,2) [x] can't place queen at (2,3) [-] removed queen at (1,0) [+] placed queen at (1,1) [>] CALL solve(2) [x] can't place queen at (2,0) [x] can't place queen at (2,1) [x] can't place queen at (2,2) [x] can't place queen at (2,3) [-] removed queen at (1,1) [x] can't place queen at (1,2) [x] can't place queen at (1,3) [-] removed queen at (0,3)