حل مشكلة Letter Combinations of a Phone Number من LeetCode بلغة Java شرح كامل باستخدام Backtracking

[@anwaraltadfi5833]

import java.util.*;
class Solution {
public List letterCombinations(String digits) {
List result = new ArrayList();
if (digits == null || digits.length() == 0) {
return result;
}
String[] mapping = {
"", // 0
"", // 1
"abc", // 2
"def", // 3
"ghi", // 4
"jkl", // 5
"mno", // 6
"pqrs",// 7
"tuv", // 8
"wxyz" // 9
};
backtrack(result, digits, mapping, 0, new StringBuilder());
return result;
}
private void backtrack(List result, String digits, String[] mapping, int index, StringBuilder current) {
if (index == digits.length()) {
result.add(current.toString());
return;
}
String letters = mapping[digits.charAt(index) - '0'];
for (char letter : letters.toCharArray()) {
current.append(letter);
backtrack(result, digits, mapping, index + 1, current);
current.deleteCharAt(current.length() - 1); // التراجع عن آخر خطوة
}
}
}