Description
Given a string S, we can transform every letter individually to be lowercase or uppercase to create another string. Return a list of all possible strings we could create.
Note:
S will be a string with length at most 12.S will consist only of letters or digits.问题描述
给定字符串S,我们可以将它的每个字母转换为大写或者小写来产生新的字符串。返回所有可以产生的字符串的列表
问题分析
回溯法
解法(backtrack)
class Solution { public List<String> letterCasePermutation(String S) { List<String> res = new ArrayList<>(); backtracking(S.toCharArray(), 0, res); return res; } private void backtracking(char[] ch, int index, List<String> res) { if(index >= ch.length) { res.add(String.valueOf(ch)); }else{ char current = ch[index]; backtracking(ch, index + 1, res); if(current >= 'A' && current <= 'Z') { ch[index] = (char)((int)'a' + (current - 'A')); backtracking(ch, index + 1, res); }else if(current >= 'a') { ch[index] = (char)((int)'A' + (current - 'a')); backtracking(ch, index + 1, res); } } } }