IsomorphicStringM1.java

import java.util.Arrays;

/**
 * Leetcode problem #205, Isomorphic Strings (Approach 1)
 * https://leetcode.com/problems/isomorphic-strings
 * 
 * Time complexity: O(n)
 * Space complexity: O(1)
 */
public class IsomorphicStringM1 {
    public static void main(String[] args) {
        String s = "paper", t = "title";
        boolean isIsomorphic = isIsomorphic(s, t);
        System.out.println(isIsomorphic);
    }

    public static boolean isIsomorphic(String s, String t) {
        if (s.length() != t.length())
            return false;

        int[] arr1 = new int[256], arr2 = new int[256];
        Arrays.fill(arr1, -1);
        Arrays.fill(arr2, -1);

        for (int i = 0; i < s.length(); i++) {
            char c1 = s.charAt(i), c2 = t.charAt(i);

            if (arr1[c1] == -1 && arr2[c2] == -1) {
                arr1[c1] = c2;
                arr2[c2] = c1;
            } else if (arr1[c1] != c2 || arr2[c2] != c1)
                return false;
        }

        return true;
    }
}