Letter Case Permutation(DFS)
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 at most12
.
S
will consist only of letters or digits.
分析
DFS。Stringbuilder做路径。 这里没有for loop但是有2条路,大写一条路小写一条路。
class Solution {
public List<String> letterCasePermutation(String S) {
List<String> ret = new ArrayList<>();
StringBuilder sb = new StringBuilder();
dfs(S,ret,sb,0);
return ret;
}
void dfs(String S, List<String> ret, StringBuilder sb, int pos){
if(pos == S.length()){
String path = sb.toString();
if(!ret.contains(path)){
ret.add(path);
}
return;
}
sb.append(Character.toLowerCase(S.charAt(pos)));
dfs(S,ret,sb,pos+1);
sb.deleteCharAt(sb.length()-1);
sb.append(Character.toUpperCase(S.charAt(pos)));
dfs(S,ret,sb,pos+1);
sb.deleteCharAt(sb.length()-1);
}
}
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