Find longest substring without repeating characters

Question

Given a string S of length N find longest substring without repeating characters.

Example:

Input:

Answer 1

Here is one more solution with only 2 string variables:

public static String getLongestNonRepeatingString(String inputStr){
    if(inputStr == null){
        return null;
    }

    String maxStr = "";
    String tempStr = "";
    for(int i=0; i < inputStr.length(); i++){
        // 1. if tempStr contains new character, then change tempStr  
        if(tempStr.contains("" + inputStr.charAt(i))){
            tempStr = tempStr.substring(tempStr.lastIndexOf(inputStr.charAt(i)) + 1);
        }
        // 2. add new character
        tempStr = tempStr + inputStr.charAt(i);
        // 3. replace maxStr with tempStr if tempStr is longer
        if(maxStr.length() < tempStr.length()){
            maxStr = tempStr;
        }
    }

    return maxStr;
}