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# Letter Combinations of a Phone Number

Updated: Apr 10, 2021

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.

A mapping of digit to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.

Example 1:

```Input: digits = "23"
```

Example 2:

```Input: digits = ""
Output: []
```

Example 3:

```Input: digits = "2"
Output: ["a","b","c"]
```

Constraints:

• 0 <= digits.length <= 4

• digits[i] is a digit in the range ['2', '9'].

Solution:

Approach 1: Iterative

```class Solution {
public List<String> letterCombinations(String digits) {
if(digits.isEmpty()) return ans;
String[] combinations = new String[] {"0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
for(int i =0; i<digits.length();i++){
int x = Character.getNumericValue(digits.charAt(i));
while(ans.get(0).length()==i){
String t = ans.remove(0);
for(char s : combinations[x].toCharArray())
}
}
return ans;
}
}
```

Approach 2: DFS

```class Solution {
String[] combinations = new String[]{"0","1","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
public List<String> letterCombinations(String digits) {
if(digits.isEmpty()) return ans;

dfs(0,new StringBuilder(),digits,ans);
return ans;
}
private void dfs(int i, StringBuilder current, String digits,List<String> ans)
{
if(i==digits.length())
{
return;
}
char curchar = digits.charAt(i);
for(char neigh:combinations[curchar-'0'].toCharArray())
{
current.append(neigh);
dfs(i+1,current,digits,ans);
current.deleteCharAt(current.length()-1);
}
}
}
```