Letter combinations of a phone number | Leetcode | Medium | Java | Striver's A to Z DSA Sheet

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This is a medium level problem on leetcode which is also a part of Striver's A to Z DSA Course/Sheet and is present in recursion section of the same.
This problem has been asked multiple times in Amazon's Online assessment.

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Shri Krishna ji ka naam leke khatam bhi kr diye !! :)😌😌

rupamsarkar

mam thoda DRY Run v karana hota hai etna fast kaun karata h

raunak_shrivastav

import java.util.*;

public class LetterCombinations {

public static void helper(int idx, String digits, Map<Character, String> mapping, StringBuilder currStr, List<String> ans) {
if (idx == digits.length()) { // Base case: if we've processed all digits
ans.add(currStr.toString());
return;
}

char ch = digits.charAt(idx); // Get the current digit
String letters = mapping.get(ch); // Get corresponding letters

for (char letter : letters.toCharArray()) { // Loop through each mapped letter
currStr.append(letter);
helper(idx + 1, digits, mapping, currStr, ans); // Recursive call
- 1); // Backtracking step
}
}

public static List<String> letterCombinations(String digits) {
List<String> ans = new ArrayList<>();
if (digits.isEmpty()) return ans; // Edge case: empty input

// Digit to letter mapping
Map<Character, String> mapping = new HashMap<>();
mapping.put('2', "abc");
mapping.put('3', "def");
mapping.put('4', "ghi");
mapping.put('5', "jkl");
mapping.put('6', "mno");
mapping.put('7', "pqrs");
mapping.put('8', "tuv");
mapping.put('9', "wxyz");

StringBuilder currStr = new StringBuilder();
helper(0, digits, mapping, currStr, ans); // Start recursion
return ans;
}

public static void main(String[] args) {
String digits = "23";
List<String> result = letterCombinations(digits);

System.out.println(result);
}
}

ChandanKumar-xdtg

How you are coming up the solution it get hard to visualize it when i am solving

ManishIndoor

mujhe toh khuch bhi smjh ni aya di. Main toh woh for loop hi tha itti jldi nipta diya

oknokok

As a add on it would be better if u could explain time complexity

iamnoob

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