isomorphic_strings.java

// https://leetcode.com/problems/isomorphic-strings/
public class Solution {
    public boolean isIsomorphic(String s, String t) {
        char[] source, target;
        char srcChar, targetChar;
        boolean isIsomorphic = true;
        
        // init two hash table
        source = new char[128];
        target = new char[128];
        for (int i = 0; i < 128; i++) {
            source[i] = 0;
            target[i] = 0;
        }
        
        int len = s.length();
        for (int i = 0; i < len; i++) {
            srcChar = s.charAt(i);
            targetChar = t.charAt(i);
            
            // whether the key is appeared the first time
            if (source[srcChar] == 0) {
                // whether the value has been mapped
                if (target[targetChar] == 0) {
                    target[targetChar] = 1;
                    source[srcChar] = targetChar;
                } else {
                    isIsomorphic = false;
                    break;
                }
            } else if (source[srcChar] != targetChar) {
                isIsomorphic = false;
                break;
            }
        }
        
        return isIsomorphic;
    }
}