【Leetcode】Isomorphic Strings

题目链接：https://leetcode.com/problems/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.

思路：

用HashMap存储字符之间映射关系，要注意是双向映射即a映射到b，b也要映射到a，用hashmap要判断两次。

算法：

 public boolean isIsomorphic(String s, String t) {
     char strs[] = s.toCharArray();
     char patterns[] = t.toCharArray();
     Map<Character, Character> maps = new HashMap<Character, Character>();

     for (int i = 0; i < strs.length; i++) {
         if (maps.containsKey(strs[i])) {
             if (!(maps.get(strs[i]).charValue() == patterns[i])) {
                 return false;
             }
         } else {
             maps.put(strs[i], patterns[i]);
         }
     }

     maps.clear();
     for (int i = 0; i < patterns.length; i++) {
         if (maps.containsKey(patterns[i])) {
             if (!(maps.get(patterns[i]).charValue() == strs[i])) {
                 return false;
             }
         } else {
             maps.put(patterns[i], strs[i]);
         }
     }
     return true;
 }