Checking if two strings are permutations of each other

Question

How to determine if two strings are permutations of each other

Answer 1

• Sort the two strings's characters.
• Compare the results to see if they're identical.

Edit:

The above method is reasonably efficient - O(n*log(n)) and, as others have shown, very easy to implement using the standard Java API. Even more efficient (but also more work) would be counting and comparing the occurrence of each character, using the char value as index into an array of counts.

I do not thing there is an efficient way to do it recursively. An inefficient way (O(n^2), worse if implemented straightforwardly) is this:

• If both strings consist of one identical character, return true
• Otherwise:
  • remove one character from the first string
  • Look through second string for occurrence of this character
  • If not present, return false
  • Otherwise, remove said character and apply algorithm recursively to the remainders of both strings.