Vzhľadom na a reťazec s úlohou je nájsť minimálne postavy byť priložené (vloženie na koniec) na vytvorenie strunového palindrómu.
Príklady:
Vstup : s = „hotovo“
Výstup : 2
Vysvetlenie: Môžeme urobiť strunový palindróm ako 'abede nie “ pridaním nie na konci šnúrky.
Vstup :s = 'aabb'
Výstup : 2
Vysvetlenie: Môžeme urobiť strunový palindróm as'aabb aa “ pridaním aa na konci šnúrky.
Obsah
- Skontrolujte palindróm zakaždým - O(n^2) čas a O(n) priestor
- Použitie algoritmu Knuth Morris Pratt - O(n) čas a O(n) priestor
Skontrolujte palindróm zakaždým - O(n^2) čas a O(n) priestor
C++Riešenie zahŕňa postupne odstránenie znakov z začiatok reťazca jeden po druhom, kým sa reťazec nestane a palindróm . Odpoveďou bude celkový počet odstránených znakov.
Zvážte napríklad reťazec s = „tu“. Najprv skontrolujeme, či celý reťazec je palindróm, ktorý nie je. Ďalej odstránime prvý znak, ktorý má za následok reťazec „prosiť“. Znova kontrolujeme, ale stále to nie je palindróm. Potom odstránime ďalší znak zo začiatku opustenie 'ede'. Tentoraz je strunou palindróm. Preto výstup je 2 predstavujúci počet znakov odstránených od začiatku na dosiahnutie palindrómu.
// C++ code to find minimum number // of appends to make string Palindrome #include using namespace std; // Function to check if a given string is a palindrome bool isPalindrome(string s) { int left = 0 right = s.length() - 1; while (left < right) { if (s[left] != s[right]) return false; left++; right--; } return true; } // Function to find the minimum number of // characters to remove from the beginning int noOfAppends(string& s) { int n = s.length(); // Remove characters from the start until // the string becomes a palindrome for (int i = 0; i < n; i++) { if (isPalindrome(s.substr(i))) { // Return the number of characters removed return i; } } // If no palindrome is found remove // all but one character return n - 1; } int main() { string s = 'abede'; int result = noOfAppends(s); cout << result << endl; return 0; }
Java // Java code to find minimum number // of appends to make string Palindrome import java.util.*; class GfG { // Function to check if a given string is a palindrome static boolean isPalindrome(String s) { int left = 0 right = s.length() - 1; while (left < right) { if (s.charAt(left) != s.charAt(right)) return false; left++; right--; } return true; } // Function to find the minimum number of // characters to remove from the beginning static int noOfAppends(String s) { int n = s.length(); // Remove characters from the start until // the string becomes a palindrome for (int i = 0; i < n; i++) { if (isPalindrome(s.substring(i))) { // Return the number of characters removed return i; } } // If no palindrome is found remove // all but one character return n - 1; } public static void main(String[] args) { String s = 'abede'; int result = noOfAppends(s); System.out.println(result); } }
Python # Python code to find minimum number # of appends to make string Palindrome # Function to check if a given string is a palindrome def is_palindrome(s): left right = 0 len(s) - 1 while left < right: if s[left] != s[right]: return False left += 1 right -= 1 return True # Function to find the minimum number of # characters to remove from the beginning def no_of_appends(s): n = len(s) # Remove characters from the start until # the string becomes a palindrome for i in range(n): if is_palindrome(s[i:]): # Return the number of characters # removed return i # If no palindrome is found remove # all but one character return n - 1 if __name__ == '__main__': s = 'abede' result = no_of_appends(s) print(result)
C# // C# code to find minimum number // of appends to make string Palindrome using System; class GfG { // Function to check if a given string // is a palindrome static bool IsPalindrome(string s) { int left = 0 right = s.Length - 1; while (left < right) { if (s[left] != s[right]) return false; left++; right--; } return true; } // Function to find the minimum number of // characters to remove from the beginning static int NoOfAppends(string s) { int n = s.Length; // Remove characters from the start until // the string becomes a palindrome for (int i = 0; i < n; i++) { if (IsPalindrome(s.Substring(i))) { // Return the number of characters // removed return i; } } // If no palindrome is found remove all but // one character return n - 1; } static void Main(string[] args) { string s = 'abede'; int result = NoOfAppends(s); Console.WriteLine(result); } }
JavaScript // JavaScript code to find minimum number // of appends to make string Palindrome // Function to check if a given string is a palindrome function isPalindrome(s) { let left = 0 right = s.length - 1; while (left < right) { if (s[left] !== s[right]) return false; left++; right--; } return true; } // Function to find the minimum number of // characters to remove from the beginning function noOfAppends(s) { let n = s.length; // Remove characters from the start until // the string becomes a palindrome for (let i = 0; i < n; i++) { if (isPalindrome(s.substring(i))) { // Return the number of // characters removed return i; } } // If no palindrome is found remove // all but one character return n - 1; } const s = 'abede'; const result = noOfAppends(s); console.log(result);
Výstup
2
Použitie algoritmu Knuth Morris Pratt - O(n) čas a O(n) priestor
C++Základnou myšlienkou tohto prístupu je, že my vypočítať a najväčší podreťazec od konca a dĺžku šnúrky mínus táto hodnota je minimálne počet príloh. Logika je intuitívna, nemusíme ju pridávať palindróm a len tie, ktoré netvoria palindróm. Aby sme našli tento najväčší palindróm od konca, my obrátene reťazec vypočíta DFA.
The DFA (deterministický konečný automat) spomínané v kontexte Algoritmus Knutha Morrisa Pratta je koncept používaný na pomoc pri hľadaní najdlhšia predpona reťazca, ktorá je zároveň príponou a znova otočte reťazec (čím získate späť pôvodný reťazec) a nájdite konečný stav, ktorý predstavuje počet zhôd reťazca s rešpektovaným reťazcom, a tak dostaneme najväčší podreťazec, ktorým je palindróm od konca.
// CPP program for the given approach // using 2D vector for DFA #include using namespace std; // Function to build the DFA and precompute the state vector<vector<int>> buildDFA(string& s) { int n = s.length(); // Number of possible characters (ASCII range) int c = 256; // Initialize 2D vector with zeros vector<vector<int>> dfa(n vector<int>(c 0)); int x = 0; dfa[0][s[0]] = 1; // Build the DFA for the given string for (int i = 1; i < n; i++) { for (int j = 0; j < c; j++) { dfa[i][j] = dfa[x][j]; } dfa[i][s[i]] = i + 1; x = dfa[x][s[i]]; } return dfa; } // Function to find the longest overlap // between the string and its reverse int longestOverlap(vector<vector<int>>& dfa string& query) { int ql = query.length(); int state = 0; // Traverse through the query to // find the longest overlap for (int i = 0; i < ql; i++) { state = dfa[state][query[i]]; } return state; } // Function to find the minimum // number of characters to append int minAppends(string s) { // Reverse the string string reversedS = s; reverse(reversedS.begin() reversedS.end()); // Build the DFA for the reversed string vector<vector<int>> dfa = buildDFA(reversedS); // Get the longest overlap with the original string int longestOverlapLength = longestOverlap(dfa s); // Minimum characters to append // to make the string a palindrome return s.length() - longestOverlapLength; } int main() { string s = 'abede'; cout << minAppends(s) << endl; return 0; }
Java // Java program for the given approach // using 2D array for DFA import java.util.*; class GfG { // Function to build the DFA and precompute the state static int[][] buildDFA(String s) { int n = s.length(); // Number of possible characters (ASCII range) int c = 256; // Initialize 2D array with zeros int[][] dfa = new int[n][c]; int x = 0; dfa[0][s.charAt(0)] = 1; // Build the DFA for the given string for (int i = 1; i < n; i++) { for (int j = 0; j < c; j++) { dfa[i][j] = dfa[x][j]; } dfa[i][s.charAt(i)] = i + 1; x = dfa[x][s.charAt(i)]; } return dfa; } // Function to find the longest overlap // between the string and its reverse static int longestOverlap(int[][] dfa String query) { int ql = query.length(); int state = 0; // Traverse through the query to // find the longest overlap for (int i = 0; i < ql; i++) { state = dfa[state][query.charAt(i)]; } return state; } // Function to find the minimum // number of characters to append static int minAppends(String s) { // Reverse the string String reversedS = new StringBuilder(s).reverse().toString(); // Build the DFA for the reversed string int[][] dfa = buildDFA(reversedS); // Get the longest overlap with the original string int longestOverlapLength = longestOverlap(dfa s); // Minimum characters to append // to make the string a palindrome return s.length() - longestOverlapLength; } public static void main(String[] args) { String s = 'abede'; System.out.println(minAppends(s)); } }
Python # Python program for the given approach # using 2D list for DFA # Function to build the DFA and precompute the state def buildDFA(s): n = len(s) # Number of possible characters (ASCII range) c = 256 # Initialize 2D list with zeros dfa = [[0] * c for _ in range(n)] x = 0 dfa[0][ord(s[0])] = 1 # Build the DFA for the given string for i in range(1 n): for j in range(c): dfa[i][j] = dfa[x][j] dfa[i][ord(s[i])] = i + 1 x = dfa[x][ord(s[i])] return dfa # Function to find the longest overlap # between the string and its reverse def longestOverlap(dfa query): ql = len(query) state = 0 # Traverse through the query to # find the longest overlap for i in range(ql): state = dfa[state][ord(query[i])] return state # Function to find the minimum # number of characters to append def minAppends(s): # Reverse the string reversedS = s[::-1] # Build the DFA for the reversed string dfa = buildDFA(reversedS) # Get the longest overlap with the # original string longestOverlapLength = longestOverlap(dfa s) # Minimum characters to append # to make the string a palindrome return len(s) - longestOverlapLength if __name__ == '__main__': s = 'abede' print(minAppends(s))
C# // C# program for the given approach // using 2D array for DFA using System; class GfG { // Function to build the DFA and precompute the state static int[] buildDFA(string s) { int n = s.Length; // Number of possible characters // (ASCII range) int c = 256; // Initialize 2D array with zeros int[] dfa = new int[n c]; int x = 0; dfa[0 s[0]] = 1; // Build the DFA for the given string for (int i = 1; i < n; i++) { for (int j = 0; j < c; j++) { dfa[i j] = dfa[x j]; } dfa[i s[i]] = i + 1; x = dfa[x s[i]]; } return dfa; } // Function to find the longest overlap // between the string and its reverse static int longestOverlap(int[] dfa string query) { int ql = query.Length; int state = 0; // Traverse through the query to // find the longest overlap for (int i = 0; i < ql; i++) { state = dfa[state query[i]]; } return state; } // Function to find the minimum // number of characters to append static int minAppends(string s) { // Reverse the string using char array char[] reversedArray = s.ToCharArray(); Array.Reverse(reversedArray); string reversedS = new string(reversedArray); // Build the DFA for the reversed string int[] dfa = buildDFA(reversedS); // Get the longest overlap with the original string int longestOverlapLength = longestOverlap(dfa s); // Minimum characters to append // to make the string a palindrome return s.Length - longestOverlapLength; } static void Main() { string s = 'abede'; Console.WriteLine(minAppends(s)); } }
JavaScript // JavaScript program for the given approach // using 2D array for DFA // Function to build the DFA and precompute the state function buildDFA(s) { let n = s.length; // Number of possible characters // (ASCII range) let c = 256; // Initialize 2D array with zeros let dfa = Array.from({ length: n } () => Array(c).fill(0)); let x = 0; dfa[0][s.charCodeAt(0)] = 1; // Build the DFA for the given string for (let i = 1; i < n; i++) { for (let j = 0; j < c; j++) { dfa[i][j] = dfa[x][j]; } dfa[i][s.charCodeAt(i)] = i + 1; x = dfa[x][s.charCodeAt(i)]; } return dfa; } // Function to find the longest overlap // between the string and its reverse function longestOverlap(dfa query) { let ql = query.length; let state = 0; // Traverse through the query to // find the longest overlap for (let i = 0; i < ql; i++) { state = dfa[state][query.charCodeAt(i)]; } return state; } // Function to find the minimum // number of characters to append function minAppends(s) { // Reverse the string let reversedS = s.split('').reverse().join(''); // Build the DFA for the reversed string let dfa = buildDFA(reversedS); // Get the longest overlap with the original string let longestOverlapLength = longestOverlap(dfa s); // Minimum characters to append // to make the string a palindrome return s.length - longestOverlapLength; } let s = 'abede'; console.log(minAppends(s));
Výstup
2
Súvisiaci článok:
- Dynamické programovanie | Sada 28 (Minimálne vloženia na vytvorenie palindrómu)