答案
Given a string s, you can transform every letter individually to be lowercase or uppercase to create another string.
Return a list of all possible strings we could create. Return the output in any order.
当前字符如果为数字，则直接添加并递归。（将字符隐式转换为整数判断是否为数字，可提升速度。）
当前字符如果为字母，则大小写分别添加到递归。（类似于回溯。）
当字符串长度与搜寻字符串相等时，添加到列表。
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| class Solution {
List<String> ans;
String _s;
public List<String> letterCasePermutation(String s) {
ans = new ArrayList();
_s = s;
backTrack(new StringBuilder(),0);
return ans;
}
private void backTrack(StringBuilder sb, int i){
if(i == _s.length()){
ans.add(sb.toString());
return;
}
char curr = _s.charAt(i);
if ( isNums(curr) ){
sb.append(curr);
backTrack(sb, i+1);
}
else{
StringBuilder sb2 = new StringBuilder(sb);
sb.append(Character.toLowerCase(curr));
backTrack(sb, i+1);
sb2.append(Character.toUpperCase(curr));
backTrack(sb2, i+1);
}
}
private boolean isNums(char c){
if ( (int)c >= (int)'0' && (int)c <= (int)'9' ){
return true;
}
return false;
}
}
|
