标签：return rac UNC transform 递归 参数 note ssi function
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.
Examples: Input: S = "a1b2" Output: ["a1b2", "a1B2", "A1b2", "A1B2"] Input: S = "3z4" Output: ["3z4", "3Z4"] Input: S = "12345" Output: ["12345"]
Note:
S will be a string with length between 1 and 12.S will consist only of letters or digits.
classical dfs
dfs helper function有三个参数，其中idx记录recursion level，当递归到最后一层时，把当前string加入res中并返回
然后判断当前字符是数字还是字母：如果是数字，直接递归到下一层并返回；如果是字母，分别转换成大、小写字母，再递归
time = O(2^n), space = O(n)
class Solution { public List<String> letterCasePermutation(String S) { List<String> res = new ArrayList<>(); if(S == null || S.length() == 0) { return res; } dfs(S, 0, res); return res; } public void dfs(String S, int idx, List<String> res) { if(idx == S.length()) { res.add(new String(S)); return; } char[] chs = S.toCharArray(); if(S.charAt(idx) >= ‘0‘ && S.charAt(idx) <= ‘9‘) { dfs(S, idx + 1, res); return; } chs[idx] = Character.toUpperCase(chs[idx]); dfs(String.valueOf(chs), idx + 1, res); chs[idx] = Character.toLowerCase(chs[idx]); dfs(String.valueOf(chs), idx + 1, res); } }
or 先把string全部转换成小写字母的char array
class Solution { public List<String> letterCasePermutation(String S) { List<String> res = new ArrayList<>(); if(S == null || S.length() == 0) { return res; } char[] chs = S.toLowerCase().toCharArray(); dfs(chs, 0, res); return res; } public void dfs(char[] chs, int idx, List<String> res) { if(idx == chs.length) { res.add(new String(chs)); return; } dfs(chs, idx + 1, res); if(Character.isLetter(chs[idx])) { chs[idx] = Character.toUpperCase(chs[idx]); dfs(chs, idx + 1, res); chs[idx] = Character.toLowerCase(chs[idx]); } } }
784. Letter Case Permutation - Easy
标签：return rac UNC transform 递归 参数 note ssi function
原文地址：https://www.cnblogs.com/fatttcat/p/11217297.html
