题目描述
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.
思路
递归,如果当前位置字符可以修改,修改或者不修改继续往下递归。
代码
class Solution {
public:
vector<string> letterCasePermutation(string S) {
vector<string> res;
//res.push_back(S);
dfs(res, S, 0);
return res;
}
void dfs(vector<string>& res, string cur, int cnt) {
if (cnt == cur.length()) {
res.push_back(cur);
return;
}
dfs(res, cur, cnt+1);
if (cur[cnt] >= '0' && cur[cnt] <= '9') return;
else if (cur[cnt] >= 'a' && cur[cnt] <= 'z') {
cur[cnt] = cur[cnt] - 'a' + 'A';
dfs(res, cur, cnt+1);
return;
}else if (cur[cnt] >= 'A' && cur[cnt] <= 'Z') {
cur[cnt] = cur[cnt] - 'A' + 'a';
dfs(res, cur, cnt+1);
return;
}
return;
}
};