LWC 72: 784. Letter Case Permutation

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/u014688145/article/details/79334475

LWC 72: 784. Letter Case Permutation

传送门：784. Letter Case Permutation

Problem:

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 most 12.
• S will consist only of letters or digits.

思路：
dfs即可，遇到数字跳过，遇到字母，分为两种情况传给子问题。

Java版本：

    public List<String> letterCasePermutation(String S) {
        all = new ArrayList<>();
        backtrack(S.toCharArray(), 0, "");
        return all;
    }

    List<String> all;
    public void backtrack(char[] cs, int pos, String ans) {
        if (pos == cs.length) {
            all.add(ans);
            return;
        }
        else {
            if (Character.isAlphabetic(cs[pos])) {
                char l = cs[pos];
                backtrack(cs, pos + 1, ans + l);
                if (l >= 'a' && l <= 'z') l = (char) (l - 'a' + 'A');
                else if (l >= 'A' && l <= 'Z') l = (char) (l - 'A' + 'a');
                backtrack(cs, pos + 1, ans + l);
            }
            else {
                backtrack(cs, pos + 1, ans + cs[pos]);
            }
        }
    }

Python版本：

class Solution(object):
    def letterCasePermutation(self, S):
        """
        :type S: str
        :rtype: List[str]
        """
        ans = []

        def dfs(S, pos, str):
            if pos == len(S):
                ans.append(str)
                return
            else:
                if S[pos].isalpha():
                    letter = S[pos]
                    dfs(S, pos + 1, str + letter.upper())
                    dfs(S, pos + 1, str + letter.lower())
                else:
                    dfs(S, pos + 1, str + S[pos])
        dfs(S, 0, '')
        return ans