[LeetCode 293] Flip Game

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 [].

solution: dfs

    @Test    public void test() {        String[] testcase = {"+","-","++","--","+++","++++","+--+","-+-+","+-+-"};        for(int i=0;i<testcase.length;i++){            System.out.println(getFlipResult(testcase[i]));        }    }    public List<String> getFlipResult(String s1) {        List<String> res = new ArrayList<String>();        if(s1.length()<2) return res;        dfs(s1, res, 0);        return res;    }    public void dfs(String s1, List<String> res, int len) {        for(int i=len;i<s1.length()-1;i++) {            if(s1.charAt(i) == '+' && s1.charAt(i) == s1.charAt(i+1)) {                String t1 = s1.substring(0, i) + "--" + s1.substring(i+2);                res.add(t1);            }else{                dfs(s1, res, i+1);            }        }    }