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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.

 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;            }}

 

205. Isomorphic Strings