Implement an algorithm to determine if a string has all unique characters. What if you cannot use additional data structures ?

gistfile1.java

/**
 * Solution 1
 * Time Complexity : O(n) where n is the length of the string
 * Space Complexity : O(1)
 * @param input
 * @return boolean
 */
public static boolean checkSingularity1(String input) {
    if(input.length() > 256) {
        return false;
    }
    boolean[] chars = new boolean[256];
    for(int i = 0; i < input.length(); i++) {
        int charIntValue = input.charAt(i);
        if(chars[charIntValue]) {
            return false;
        }
        chars[charIntValue] = true;
    }
    return true;
}

/**
 * Solution 2
 * Time Complexity : O(n) where n is the length of the string
 * Space Complexity : O(1)
 * @param input
 * @return boolean
 */
public static boolean checkSingularity2(String input) {
    if(input.length() > 256) {
        return false;
    }
    int checker = 0;
    for(int i = 0; i < input.length(); i++) {
        int val = input.charAt(i) - 'a';
        if((checker & (1 << val)) > 0) {
            return false;
        }
        checker |= (1 << val);
    }
    return true;
}