leetcode 205. Isomorphic Strings

题目

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.

解

public class Solution {
public boolean isIsomorphic(String s, String t) {

if(s==null && t==null)
return true;
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)){//包含在映射中
if(map.get(c1)!=c2)
return false;
}else{
if(set.contains(c2)){
//不包含在映射中，但是已经该值已经被其他键对应过，
//属于多对一的情况
return false;
}else{
map.put(c1, c2);
set.add(c2);
}
}
}

return true;

}
}

参考链接

http://blog.csdn.net/xudli/article/details/45386777

http://blog.csdn.net/DERRANTCM/article/details/48021425