g0701_0800.s0784_letter_case_permutation.Solution Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of leetcode-in-java21 Show documentation

Java-based LeetCode algorithm problem solutions, regularly updated

There is a newer version: 1.38

package g0701_0800.s0784_letter_case_permutation;

// #Medium #String #Bit_Manipulation #Backtracking #Algorithm_I_Day_11_Recursion_Backtracking
// #2022_03_26_Time_10_ms_(40.38%)_Space_55.5_MB_(5.44%)

import java.util.ArrayList;
import java.util.List;

/**
 * 784 - Letter Case Permutation\.
 *
 * Medium
 *
 * 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.
**/
public class Solution {
    private List ans = new ArrayList<>();

    public List letterCasePermutation(String s) {
        helper(s, 0, "");
        return ans;
    }

    public void helper(String s, int curr, String temp) {
        if (curr == s.length()) {
            ans.add(temp);
            return;
        }
        if (Character.isDigit(s.charAt(curr))) {
            helper(s, curr + 1, temp + s.charAt(curr));
        } else {
            if (Character.isLowerCase(s.charAt(curr))) {
                helper(s, curr + 1, temp + s.charAt(curr));
                helper(s, curr + 1, temp + (s.substring(curr, curr + 1)).toUpperCase());
            } else {
                helper(s, curr + 1, temp + s.charAt(curr));
                helper(s, curr + 1, temp + (s.substring(curr, curr + 1)).toLowerCase());
            }
        }
    }
}