Topcoder711B

Problem Statement

You are given the Strings s and t. Both strings have the same length.

You are allowed to modify s. In each step you may choose two valid indices i and j such that i > j, and change s[i] to s[j]. For example, if s = "abc", you may choose i=2 and j=0, which will change s to "aba".

Return "Possible" (quotes for clarity) if you can change s into t by a sequence of zero or more steps. Otherwise, return "Impossible".

Note that the return values are case-sensitive.

Definition

Class:	StringTransform
Method:	isPossible
Parameters:	String, String
Returns:	String
Method signature:	String isPossible(String s, String t)
(be sure your method is public)

Limits

Time limit (s):	2.000
Memory limit (MB):	512
Stack limit (MB):	512

Constraints

-

s will contain between 1 and 1,000 characters, inclusive.

-

s and t will be of equal length.

-

s will contain only lowercase English letters.

-

t will contain only lowercase English letters.

Examples

0)

"abc"

"aba"

Returns: "Possible"

This is the example from the problem statement. We can change s into t by changing s[2] to s[0].

1)

"abc"

"bbc"

Returns: "Impossible"

Note that in each step i must be greater than j. You are not allowed to choose i=0 and j=1.

2)

"topcoder"

"topcoder"

Returns: "Possible"

The two strings are equal, so we don't have to make any changes.

3)

"rdmcxnnbbe"

"rdrrxrnxbe"

Returns: "Possible"

4)

"rdmcxnnbbe"

"rdqrxrnxbe"

Returns: "Impossible"

import java.util.*;
public class StringTransform {
   
    public static String isPossible(String s,String t){
        Set<Character> set = new HashSet<Character>();
      set.clear();
        for(int i=0;i<s.length();++i) {
           
            if (s.charAt(i) != t.charAt(i)) {
                if (!set.contains(t.charAt(i)))
                    return "Impossible";
            }
                set.add(s.charAt(i));
                
            }
        
        return "Possible";

    }
}