205. Isomorphic Strings

Posted 2020-08-09 Machelsky

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.

 Solution1:

思路：用map来map对应的char。注意特殊情况aa,ab. 要记录t的字母是否遇到过，用一个boolean array来检查。

public class Solution {
    public boolean isIsomorphic(String s, String t) {
        if(s.length()!=t.length())
        {
            return false;
        }
        boolean[] check=new boolean[128];
        Map<Character,Character> res=new HashMap<Character,Character>();
        for(int i=0;i<s.length();i++)
        {
            char a=s.charAt(i);
            char b=t.charAt(i);
            if(!res.containsKey(a))
            {
                if(check[b])
                {
                    return false;
                }
                res.put(a,b);
                check[b]=true;
            }
            else
            {
                if(b==res.get(a))
                {
                    continue;
                }
                else
                {
                    return false;
                }
            }
        }
        return true;
        
    }
}

Solution2:用双map来一一对应。

Solution3:

Isomorphic strings, word pattern这类题都可以用map的containsvalue,containskey来做，很省事。

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