205. Isomorphic Strings(字符串同构)

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.

Example 1:

Input: s = "egg", t = "add"
Output: true

Example 2:

Input: s = "foo", t = "bar"
Output: false

Example 3:

Input: s = "paper", t = "title"
Output: true

解释：就是像以前语文题的 aabb型  开开心心和快快乐乐就是字符同构。
方法一：记录摆放位置

public boolean isIsomorphic(String s, String t) {
    int[] preIndexOfS = new int[256];
    int[] preIndexOfT = new int[256];
    for (int i = 0; i < s.length(); i++) {
        char sc = s.charAt(i), tc = t.charAt(i);
        if (preIndexOfS[sc] != preIndexOfT[tc]) {
            return false;
        }
        preIndexOfS[sc] = i + 1;
        preIndexOfT[tc] = i + 1;
    }
    return true;
}

方法二：用hashMap记录对应关系

public class Solution {
    public boolean isIsomorphic(String s, String t) {
        
        HashMap<Character,Character> map=new HashMap<Character,Character>();
        for(int i=0;i<s.length();i++){
            char a=s.charAt(i),b=t.charAt(i);
            if(map.containsKey(a)){
                if(map.get(a)!=b){
                    return false;
                }
            }else{
                if(!map.containsValue(b)){
                    map.put(a,b);
                }else{
                    return false;
                }
            }
        }
        return true;
    }
}