Flip Game I && II

Flip Game I

Problem Description:

You are playing the following Flip Game with your friend: Given a string that contains only these two characters: + and -, you and your friend take turns to flip two consecutive "++" into "--". The game ends when a person can no longer make a move and therefore the other person will be the winner.

Write a function to compute all possible states of the string after one valid move.

For example, given s = "++++", after one move, it may become one of the following states:

[
  "--++",
  "+--+",
  "++--"
]

If there is no valid move, return an empty list [].

     public List<String> generatePossibleNextMoves(String s) {
         List<String> list = new ArrayList<String>();

         if (s == null || s.length() < ) return list;

         for (int i = -; (i = s.indexOf("++", i + )) >= ;) {
             list.add(s.substring(, i) + "--" + s.substring(i + ));
         }
         return list;
     }

Flip Game II

Problem Description:

You are playing the following Flip Game with your friend: Given a string that contains only these two characters: + and -, you and your friend take turns to flip two consecutive "++" into "--". The game ends when a person can no longer make a move and therefore the other person will be the winner.

Write a function to determine if the starting player can guarantee a win.

For example, given s = "++++", return true. The starting player can guarantee a win by flipping the middle "++" to become "+--+".

Code is from: https://discuss.leetcode.com/topic/27287/short-java-ruby?show=64350

     public boolean canWin(String s) {
         for (int i=-; (i = s.indexOf("++", i+)) >= ; )
             if (!canWin(s.substring(, i) + "-" + s.substring(i + ))) return true;
         return false;
     }