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 checkif(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;}}

，两粒种子，一片森林。