IsomorphicStrings(leetcode205)

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

// 这里我维护两个 map来处理映射，因为要求一个元素只能对一种元素
public static boolean isIsomorphic(String s, String t) {
    Map<Character,Character> map =  new HashMap<>();
    Map<Character,Character> map2 =  new HashMap<>();

    if(s.length() != t.length()){
        return false;
    }
    for(int i = 0;i< s.length();i++){
        Character c = s.charAt(i);
        Character c2 = t.charAt(i);
        if(map.containsKey(c)){
             if(!c2.equals(map.get(c))){
                 return false;
             }
        }else{
            map.put(c,c2);
        }
    }
    for(int i = 0;i< t.length();i++){
        Character c = t.charAt(i);
        Character c2 = s.charAt(i);
        if(map2.containsKey(c)){
            if(!c2.equals(map2.get(c))){
                return false;
            }
        }else{
            map2.put(c,c2);
        }
    }
    return true;
}

//在相应位置维护一个值
public static boolean isIsomorphic2(String s1, String s2) {
    int[] m = new int[512];
    for (int i = 0; i < s1.length(); i++) {
        if (m[s1.charAt(i)] != m[s2.charAt(i)+256]) {
            return false;
        }
        m[s1.charAt(i)] = m[s2.charAt(i)+256] = i+1;
    }
    return true;
}

//利用了 map的put特性 @return previous value, or null if none
public static boolean isIsomorphic3(String s, String t) {
    Map m = new HashMap();
    for (Integer i=0; i<s.length(); ++i) {
        if (m.put(s.charAt(i), i) != m.put(t.charAt(i)+"", i)) {
            return false;
        }
    }
    return true;
}

git：https://github.com/woshiyexinjie/leetcode-xin/tree/master/src/main/java/com/helloxin/leetcode/algorithms