205. Isomorphic Strings

Problem

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.

Solution

class Solution {
    public boolean isIsomorphic(String s, String t) {
        int[] map = new int[128];
        char[] str = s.toCharArray();
        char[] tar = t.toCharArray();
        int n = str.length;
        for (int i = 0; i < n; i++) {
            if (map[tar[i]] == 0) {
                if (search(map, str[i], tar[i]) != -1) {
                    return false;
                }
                map[tar[i]] = str[i];
            } else {
                if (map[tar[i]] != str[i]) {
                    return false;
                }
            }
        }
        return true;
    }

    private int search(int[] map, int tar, int skip) {
        for (int i = 0; i < 128; i++) {
            if (i == skip) {
                continue;
            }
            if (map[i] != 0 && map[i] == tar) {
                return i;
            }
        }
        return -1;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).