Can someone explain this code? Permutation code [closed]

Answer 1

permutations(prefix + s.charAt(i), s.substring(0, i) + s.substring(i+1, n));

Actually, this permutation algorithm is using the idea of

Switching current character with ith character.

Suppose we have a string abc. So the permutation of it is:

abc, acb, bac, bca, cab, cba

We can find that the acb is just switching b and c in abc with prefix a. And the bca is just switching c and a in bac with prefix b.

Then we just use the same idea to recursively solve permutation problem.