Two strings are isomorphic if the characters in s can be replaced to gett.
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.
建1个map保存映照关系,同时用1个set保持 被映照的char,保证同1个char 不会被映照两次.
[CODE]
public class Solution {
//test case: "egg","add"
public boolean isIsomorphic(String s,String t) {
//init check
if(s==null || t==null) return false;
if(s.length() != t.length()) return false;
Map<Character,Character> map = new HashMap<Character,Character>();
Set<Character> set = new HashSet<Character>();
for(int i=0; i<s.length(); i++) {
char c1 = s.charAt(i);
char c2 = t.charAt(i);
if(map.containsKey(c1)) {
if(map.get(c1) != c2) return false;
} else {
if(set.contains(c2)) return false;
else {
map.put(c1,c2);
set.add(c2);
}
}
}
return true;
}
}
