LeetCode | 784. Letter Case Permutation

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题目

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.

Example 1:

Input: s = “a1b2”
Output: [“a1b2”,“a1B2”,“A1b2”,“A1B2”]

Example 2:

Input: s = “3z4”
Output: [“3z4”,“3Z4”]

Constraints:

1 <= s.length <= 12
s consists of lowercase English letters, uppercase English letters, and digits.

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代码

class Solution {
    
    
public:
    void backtrack(string S, int idx, set<string>& res) {
    
    
        if(idx == S.length())
        {
    
    
            res.insert(S);
            return;
        }
        for(int i = idx; i<S.length(); i++)
        {
    
    
            if(S[i] >= '0' && S[i] <= '9')
                continue;
            else
            {
    
    
                S[i] ^= (1<<5);
                res.insert(S);
                backtrack(S, i+1, res);
                S[i] ^= (1<<5);
            }
        }
        
        return;
    }
    vector<string> letterCasePermutation(string S) {
    
    
        vector<string> res;
        set<string> res_set;
        if(S.length() < 1)
            return res;
        res_set.insert(S);
        for(int i = 0; i<S.length(); i++)
        {
    
    
            if(S[i] <= '9' && S[i] >= '0')
                continue;
            backtrack(S, i, res_set);
        }
        for(set<string>::iterator iter = res_set.begin(); iter!=res_set.end(); iter++)
            res.push_back(*iter);
        return res;
    }
};

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