[LeetCode] 205. Isomorphic Strings

Problem

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
Note:
You may assume both s and t have the same length.

Solution

Using HashMap

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

Using Array to replace Map

class Solution {
    public boolean isIsomorphic(String s, String t) {
        int[] stmap = new int[256];
        int[] tsmap = new int[256];
        Arrays.fill(stmap, -1);
        Arrays.fill(tsmap, -1);
        for (int i = 0; i < s.length(); i++) {
            if (stmap[s.charAt(i)] != tsmap[t.charAt(i)]) return false;
            stmap[s.charAt(i)] = i;
            tsmap[t.charAt(i)] = i;
        }
        return true;
    }
}