DFS -- Backtracking (cont.)

stack -> --------- 1 1 2 1 2 5 1 2 5 6 1 2 5 6 8 1 2 5 6 1 2 5 1 2 1 1 3 1 3 9 1 3 9 7 1 3 9 1 3 9 12 1 3 9 12 10 1 3 9 12 10 11