205_Isomorphic_Strings.swift

/*
 Done 25.09.2025. Revisited: N/A

 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
 Explanation:
 The strings s and t can be made identical by:
 - Mapping 'e' to 'a'.
 - Mapping 'g' to 'd'.

 Example 2:
 Input: s = "foo", t = "bar"
 Output: false
 Explanation:
 The strings s and t can not be made identical as 'o' needs to be mapped to both 'a' and 'r'.

 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.

 https://www.youtube.com/watch?v=7yF-U1hLEqQ
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 */

import Foundation

class P205 {

    // MARK: - Option 1 (my). Time: O(n). Memory: O(?)

    func isIsomorphic(_ s: String, _ t: String) -> Bool {
        // TODO: Incomplete solution

        if s.count != t.count { return false }
        var charsMapping = [Character: Character]()

        for i in 0..<s.count {
            if let ch = charsMapping[s[i]] {
                if ch != t[i] {
                    return false
                }
            } else {
                if let ch = charsMapping[t[i]] {
                    if ch != s[i] {
                        return false
                    }
                }
                charsMapping[s[i]] = t[i]
            }
        }

        return true
    }

    // MARK: - Option 2 (neetcode). Time: O(n). Memory: O(n)

    func isIsomorphic2(_ s: String, _ t: String) -> Bool {
        var mapST: [Character: Character] = [:]
        var mapTS: [Character: Character] = [:]

        for i in 0..<s.count {
            let c1 = s[i]
            let c2 = t[i]

            if (mapST[c1] != nil && mapST[c1] != c2) || (mapTS[c2] != nil && mapTS[c2] != c1) {
                return false
            }

            mapST[c1] = c2
            mapTS[c2] = c1
        }

        return true
    }

}