[LeetCode] 784. Letter Case Permutation

轉自LeetCode

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.

<Solution>

想法如下

• 看到排列組合，第一個直覺是用 dfs 來解

• 首先，先一路一直走到底。然後回頭的時候，檢查當下的字元是數字還是字母，是字母的話，根據他的大小寫，再做 dfs 下去

code 如下

Java

	class Solution {
	private List<String> ans;
	public List<String> letterCasePermutation(String S) {
	ans = new ArrayList<>();
	final int len = S.length();
	permutation("", S, 0, len);
	return ans;
	}
	private void permutation(String output, final String s, final int index, final int len) {
	if(index == len) {
	ans.add(output);
	return;
	}
	final char c = s.charAt(index);
	permutation(output + c, s, index+1, len);
	if(Character.isLetter(c)) {
	permutation(output + (Character.isUpperCase(c) ? Character.toLowerCase(c) : Character.toUpperCase(c)), s, index+1, len);
	}
	}
	}

view raw letterCasePermutation.java hosted with ❤ by GitHub