Isomorphic Strings

Given two strings s and t, determine if they are isomorphic.

Two strings are isomorphic if the characters in s can be replaced to get t.

All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character but a character may map to itself.

For example,
Given "egg", "add", return true.

Given "foo", "bar", return false.

Given "paper", "title", return true.

这题需要注意的地方是我们要从S到T 和T到S都检查一遍。

public class Solution {
    public boolean isIsomorphic(String s, String t) {
        if (s.length() != t.length()) return false;
        
        Map<Character, Character> map = new HashMap<>();
        
        for (int i = 0; i < s.length(); i++) {
            char chKey = s.charAt(i);
            char chValue = t.charAt(i);
            
            if(map.containsKey(chKey)) {
                char value = map.get(chKey);
                if (value != chValue) {
                    return false;
                }
            } else {
                map.put(chKey, chValue);
            }
        }
        
        map.clear();
        
        for (int i = 0; i < s.length(); i++) {
            char chKey = t.charAt(i);
            char chValue = s.charAt(i);
            
            if(map.containsKey(chKey)) {
                char value = map.get(chKey);
                if (value != chValue) {
                    return false;
                }
            } else {
                map.put(chKey, chValue);
            }
        }
        
        return true;
    }
}