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 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.

题目含义： 给定两个字符串s和t，确定它们是否是同构的。如果s中的元素被替换可以得到t，那么称这两个字符串是同构的。在用一个字符串的元素替换另一个字符串的元素的过程中，所有字符的顺序必须保留。

方法一：

    public boolean isIsomorphic(String s, String t) {
        int[] m1 = new int[256];
        int[] m2 = new int[256];
        int n = s.length();
        for (int i = 0; i < n; ++i) {
            int schar = s.charAt(i);
            int tchar = t.charAt(i);
            if (m1[schar] != m2[tchar]) return false;
            m1[schar] = i + 1;
            m2[tchar] = i + 1;
        }
        return true;        
    }

方法二：

    private static boolean isIsomorphic(String left, String right){
        Map<Character,Character> map = new HashMap<>();
        if (left.length() !=right.length()) return false;
        for (int i=0;i<left.length();i++){
            Character l = left.charAt(i);
            Character r = right.charAt(i);

            if (map.containsKey(l)){
                if (!r.equals(map.get(l))) {
//                    l对于了多个r
                    return false;
                }
                continue;
            }
            //r出现了，但是l没有出现
            if (map.containsValue(r)){
                return false;
            }
            map.put(l,r);
        }
        return true;
    }