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.

哈希表法

复杂度

时间 O(N) 空间 O(N)

思路

用一个哈希表记录映射关系，一个集合记录已经映射过的字母。或者用两个哈希表记录双向的映射关系。

代码

public class Solution {    public boolean isIsomorphic(String s, String t) {        Map<Character, Character> map = new HashMap<Character, Character>();        Set<Character> set = new HashSet<Character>();        if(s.length() != t.length()) return false;        for(int i = 0; i < s.length(); i++){char sc = s.charAt(i), tc = t.charAt(i);if(map.containsKey(sc)){    if(tc != map.get(sc)) return false;} else {    if(set.contains(tc)) return false;    map.put(sc, tc);    set.add(tc);}        }        return true;    }}