Donada una matriu de cadenes (totes les lletres minúscules), la tasca és agrupar-les de tal manera que totes les cadenes d'un grup siguin versions desplaçades entre si.
Dues cordes s1 i s2 s'anomenen desplaçats si es compleixen les condicions següents:
- s1.longitud és igual a s2.longitud
- s1[i] és igual a s2[i] + m per a tots 1<= i <= s1.length for a constant nombre enter m. Considereu que el desplaçament és cíclic, és a dir, si s2[i] + m > 'z', comenceu des de 'a' o si s2[i] + m< 'a' then start from 'z'.
Exemples:
Entrada: arr[] = ['acd' 'dfg' 'wyz' 'yab' 'mop' 'bdfh' 'a' 'x' 'moqs']
Sortida: [ ['acd' 'dfg' 'wyz' 'yab' 'mop'] ['bdfh' 'moqs'] ['a' 'x'] ]
Explicació: Totes les cadenes desplaçades s'agrupen.
Entrada: arr = ['friki' 'per a' 'frikis']
Sortida: [['per'] ['friki'] ['friquis']]
Enfocament: Ús de Hash Map
C++La idea és generar un únic haixix per a cada grup per normalitzant les cordes. Aquí normalitzant significa fer que el primer caràcter de cada cadena sigui igual a 'a' calculant el necessari torns i aplicant-lo de manera uniforme a tots els personatges moda cíclica .
Exemple: s = 'dca' canvis = 'd' - 'a' = 3
caràcters normalitzats: "d" - 3 = "a" "c" - 3 = "z" i "a" - 3 = "x"
cadena normalitzada = 'azx'El cadena normalitzada (hash) representa el patró de canvi de manera que les cadenes amb el mateix patró tinguin el mateix hash. Utilitzem un mapa hash per fer un seguiment d'aquests hash i assignar-los als grups corresponents. Per a cada cadena calculem un hash i l'utilitzem per crear un grup nou o afegir la cadena a un grup existent en un sol recorregut.
// C++ program to print groups of shifted strings // together using Hash Map #include
// Java program to print groups of shifted strings // together using Hash Map import java.util.*; class GfG { // Function to generate hash by shifting and equating the // first character static String getHash(String s) { // Calculate the shift needed to normalize the string int shifts = s.charAt(0) - 'a'; char[] chars = s.toCharArray(); for (int i = 0; i < chars.length; i++) { // Adjust each character by the shift chars[i] = (char) (chars[i] - shifts); // Wrap around if the character goes below 'a' if (chars[i] < 'a') chars[i] += 26; } return new String(chars); } // Function to group shifted strings together static ArrayList<ArrayList<String>> groupShiftedString(String[] arr) { ArrayList<ArrayList<String>> res = new ArrayList<>(); // Maps hash to index in result HashMap<String Integer> mp = new HashMap<>(); for (String s : arr) { // Generate hash representing the shift pattern String hash = getHash(s); // If new hash create a new group if (!mp.containsKey(hash)) { mp.put(hash res.size()); res.add(new ArrayList<>()); } // Add string to its group res.get(mp.get(hash)).add(s); } return res; } public static void main(String[] args) { String[] arr = {'acd' 'dfg' 'wyz' 'yab' 'mop' 'bdfh' 'a' 'x' 'moqs'}; ArrayList<ArrayList<String>> groups = groupShiftedString(arr); for (ArrayList<String> group : groups) { for (String s : group) { System.out.print(s + ' '); } System.out.println(); } } }
# Python program to print groups of shifted strings # together using Hash Map # Function to generate hash by shifting and equating the first character def getHash(s): # Calculate the shift needed to normalize the string shifts = ord(s[0]) - ord('a') hashVal = [] for ch in s: # Adjust each character by the shift newCh = chr(ord(ch) - shifts) # Wrap around if the character goes below 'a' if newCh < 'a': newCh = chr(ord(newCh) + 26) hashVal.append(newCh) return ''.join(hashVal) # Function to group shifted strings together def groupShiftedString(arr): res = [] # Maps hash to index in result mp = {} for s in arr: # Generate hash representing the shift pattern hashVal = getHash(s) # If new hash create a new group if hashVal not in mp: mp[hashVal] = len(res) res.append([]) # Add string to its group res[mp[hashVal]].append(s) return res if __name__ == '__main__': arr = ['acd' 'dfg' 'wyz' 'yab' 'mop' 'bdfh' 'a' 'x' 'moqs'] groups = groupShiftedString(arr) for group in groups: print(' '.join(group))
// C# program to print groups of shifted strings // together using Hash Map using System; using System.Collections.Generic; class GfG { // Function to generate hash by shifting and equating the first character static string getHash(string s) { // Calculate the shift needed to normalize the string int shifts = s[0] - 'a'; char[] chars = s.ToCharArray(); for (int i = 0; i < chars.Length; i++) { // Adjust each character by the shift chars[i] = (char)(chars[i] - shifts); // Wrap around if the character goes below 'a' if (chars[i] < 'a') chars[i] += (char)26; } return new string(chars); } // Function to group shifted strings together static List<List<string>> groupShiftedString(string[] arr) { List<List<string>> res = new List<List<string>>(); // Maps hash to index in result Dictionary<string int> mp = new Dictionary<string int>(); foreach (string s in arr) { // Generate hash representing the shift pattern string hash = getHash(s); // If new hash create a new group if (!mp.ContainsKey(hash)) { mp[hash] = res.Count; res.Add(new List<string>()); } // Add string to its group res[mp[hash]].Add(s); } return res; } static void Main(string[] args) { string[] arr = { 'acd' 'dfg' 'wyz' 'yab' 'mop' 'bdfh' 'a' 'x' 'moqs' }; var groups = groupShiftedString(arr); foreach (var group in groups) { Console.WriteLine(string.Join(' ' group)); } } }
// JavaScript program to print groups of shifted strings // together using Hash Map // Function to generate hash by shifting and equating the first character function getHash(s) { // Calculate the shift needed to normalize the string const shifts = s.charCodeAt(0) - 'a'.charCodeAt(0); let chars = []; for (let ch of s) { // Adjust each character by the shift let newChar = String.fromCharCode(ch.charCodeAt(0) - shifts); // Wrap around if the character goes below 'a' if (newChar < 'a') newChar = String.fromCharCode(newChar.charCodeAt(0) + 26); chars.push(newChar); } return chars.join(''); } // Function to group shifted strings together function groupShiftedString(arr) { const res = []; // Maps hash to index in result const mp = new Map(); for (let s of arr) { // Generate hash representing the shift pattern const hash = getHash(s); // If new hash create a new group if (!mp.has(hash)) { mp.set(hash res.length); res.push([]); } // Add string to its group res[mp.get(hash)].push(s); } return res; } // Driver Code const arr = ['acd' 'dfg' 'wyz' 'yab' 'mop' 'bdfh' 'a' 'x' 'moqs']; const groups = groupShiftedString(arr); groups.forEach(group => console.log(group.join(' ')));
Sortida
acd dfg wyz yab mop bdfh moqs a x
Complexitat temporal: O(n*k) on n és la longitud de la matriu de cadenes i k és la longitud màxima d'una cadena en la matriu de cadenes.
Espai auxiliar: O(n*k) en el pitjor dels casos podríem generar n cadenes hash diferents respectivament per a cada cadena d'entrada. Així, hem obtingut n entrades diferents al mapa hash cadascuna de longitud k o menys.