Write code for the tree_iter type (struct) and the ti_create, ti_done, ti_next, ti_val, and ti_delete functions employed in Example 6.73. Write, in C#, Python, or Ruby, an iterator that yields (a) all...

Write code for the tree_iter type (struct) and the ti_create, ti_done, ti_next, ti_val, and ti_delete functions employed in Example 6.73. Write, in C#, Python, or Ruby, an iterator that yields (a) all permutations of the integers 1 . . n (b) all combinations of k integers from the range 1 . . n (0 ≤ k ≤ n). You may represent your permutations and combinations using either a list or an array.