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Letter Case Permutation

Tags : string, recursion, leetcode, cpp, medium

Problem Statement - link #

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. You can return the output in any order.

Examples #

Example 1:

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

Example 2:

Input: s = "3z4"
Output: ["3z4","3Z4"]

Example 3:

Input: s = "12345"
Output: ["12345"]

Example 4:

Input: s = "0"
Output: ["0"]

Constraints #

Solutions #


class Solution {
public:
    vector<string> ans;
    
    void recurse(int i, string &s){
        if(i == s.size()){
            ans.push_back(s);
            return ;
        }
        for(int j=i; j<s.size(); j++){
            if(s[j] >= '0' && s[j]<='9'){
                continue;                
            }
            else if(s[j] >='a' && s[j]<='z'){
                s[j] = (s[j] - 'a') + 'A';
                recurse(j+1,s);
                s[j] = (s[j] - 'A') + 'a';
            }else{
                s[j] = (s[j] - 'A') + 'a';
                recurse(j+1,s);
                s[j] = (s[j] - 'a') + 'A';
            }            
        }

        ans.push_back(s);
        return;
    }
    
    vector<string> letterCasePermutation(string s) {
        
        recurse(0,s);
        return ans;
    
    }
};