GetSubsequence | Topcoder Archive

Problem Statement

Given a String s, we will first collect all distinct positive length subsequences of s, and place them in a list L. A subsequence of s is obtained by deleting 0 or more characters. Next, sort L into ascending order by length. Where ties occur, break them lexicographically. Here uppercase letters occur before lowercase letters. Finally, return the String in position pos % k (0-based), where k is the number of elements in L, and % is the modulus operator.

Definition

Class:: GetSubsequence
Method:: getAt
Parameters:: String, String
Returns:: String
Method signature:: String getAt(String s, String pos)
(be sure your method is public)

Constraints

s will contain between 2 and 50 characters inclusive.
Each character in s will be a letter ('A'-'Z','a'-'z').
pos will be an integral value between 0 and 2^63 - 1 inclusive.
pos will not have extra leading zeros.

Examples

```
"ABCD"
```
```
"14"
```
```
Returns: "ABCD"
```
"ABCD" is the last of the 15 subsequences in L.
```
"ABCD"
```
```
"19203410239121"
```
```
Returns: "ABD"
```
19203410239121 % 15 = 11.

"AAAAAAAAAAAA"

"10"

Returns: "AAAAAAAAAAA"

"AbcdAbcdAbcd"

"39283423984923"

Returns: "AbAbdbd"

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