#leetcode#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.

Note:

You may assume both s and t have the same length.

public class Solution {
public boolean isIsomorphic(String s, String t) {
if(s == null && t == null)
return true;
if(s == null || t == null)
return false;

Map<Character, Character> map1 = new HashMap<>();
Map<Character, Character> map2 = new HashMap<>();

for(int i = 0; i < s.length(); i++){
char sChar = s.charAt(i);
char tChar = t.charAt(i);

if(!map1.containsKey(sChar)){
map1.put(sChar, tChar);
}else{
if(tChar != map1.get(sChar)){
return false;
}
}

if(!map2.containsKey(tChar)){
map2.put(tChar, sChar);
}else{
if(sChar != map2.get(tChar)){
return false;
}
}
}
return true;
}
}

注意： 要求双向对应， 比如 ‘ab’ 对应 ‘aa’应该返回false， 所以用了两个hashmap