python3

javascript

java

Remove Duplicate Letters

Given a string s, remove duplicate letters so that every letter appears once and only once. 

You must make sure your result is the smallest in lexicographical order among all possible results.

### Input Format:
First Parameter - String `s` 
### Output Format:
Return a string that is the smallest in lexicographical order among all possible results

### Example 1:
```
Input: bcabc
Output: abc
```

### Example 2:
```
Input: devsnest
Output: devnst
```
### Constraints:-
+ 1 <= length of string <= 10^4^
+ string consists of lowercase English letters.
+ Expected Time Complexity:- O(n)
+ Expected Space Complexity: O(n)

static String solve(String s){
//CODE HERE 
}