leetcode 205: 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 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.

[思路]

建一个map保存映射关系, 同时用一个set保持 被映射的char, 保证同一个char 不会被映射两次.

[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;
}
}