0205. Isomorphic Strings

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Given two strings s and t, determine if they are isomorphic.

Two strings s and t 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

Constraints:

• 1 <= s.length <= 5 * 10^4
• t.length == s.length
• s and t consist of any valid ascii character.

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解法1

判断s和t中的字符是否是一一对应, 没有多对一的情况. 那么判断两次就好了.

class Solution {
    public boolean isIsomorphic(String s, String t) {
        if(s.length() != t.length())
            return false;
        
        return helper(s, t) && helper(t, s);
    }
    
    private boolean helper(String s, String t){
        Map<Character, Character> map = new HashMap<>();
        for(int i = 0, len = s.length(); i < len; i++){
            char cs = s.charAt(i), ct = t.charAt(i);
            if(!map.containsKey(cs))
                map.put(cs, ct);
            else if(map.get(cs) != ct)
                return false;
        }
        return true;
    }
}