131-分割回文串

public class one_three_one_分割回文串 {

    @Test
    public void test(){
        String s = "";
        partition(s);
        System.out.println(res.toString());
    }

    private List<List<String>> res = new ArrayList<>();

    public List<List<String>> partition(String s) {
        backtrace(s, new ArrayList<>(), 0);
        return res;
    }

    public void backtrace(String s, List<String> path, int splitIndex){
        if (splitIndex == s.length()){	//结束条件：分割到底
            res.add(new ArrayList<>(path));
            return ;
        }
        for (int i = splitIndex; i < s.length(); i++) {
            String a = s.substring(splitIndex, i + 1);	//做选择
            path.add(a);
            if (check(a)){	//条件递归
                backtrace(s, path, i + 1);
            }
            path.remove(path.size() - 1);	//撤销选择
        }
    }

    //检验回文
    public boolean check(String str){
        for (int i = 0; i < str.length() / 2; i++) {
            if (str.charAt(i) != str.charAt(str.length() - i - 1)) return false;
        }
        return true;
    }
}

public void backtrace(String s, List<String> path, int splitIndex){
    if (splitIndex == s.length()){
        res.add(new ArrayList<>(path));
        return ;
    }
    for (int i = splitIndex; i < s.length(); i++) {
        String a = s.substring(splitIndex, i + 1);
        if (!check(a)) continue;	//先判断不回文，减少一次add和remove操作
        path.add(a);
        backtrace(s, path, i + 1);
        path.remove(path.size() - 1);
    }
}