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Número mínimo de acréscimos necessários para fazer um palíndromo de string

Dado um cadeia de caracteres a tarefa é encontrar mínimo personagens para serem anexado (inserção no final) para fazer um palíndromo de cordas. 

Exemplos:  

Entrada :s = ‘feito’
Saída : 2
Explicação: Podemos fazer um palíndromo de cordas como 'abede não 'adicionando não no final da string.

Entrada :s = 'aabb'
Saída : 2
Explicação: Podemos fazer um palíndromo de cordas como'aabb ah 'adicionando ah no final da string.



Índice

Verifique o palíndromo sempre - O (n ^ 2) Tempo e O (n) Espaço

A solução envolve progressivamente removendo caracteres do começo da corda, um por um, até que a corda se torne um palíndromo . A resposta será o número total de caracteres removidos.

Por exemplo, considere a string s = ‘aqui’. Primeiro verificamos se a string inteira é um palíndromo, o que não é. Em seguida, removemos o primeiro caractere resultando no string 'implorar'. Verificamos novamente, mas ainda não é um palíndromo. Em seguida, removemos outro personagem desde o início deixando 'ede'. Desta vez a string é um palíndromo. Portanto o a saída é 2 representando o número de caracteres removidos desde o início para obter um palíndromo.

C++
// 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); 

Saída
2 

Usando o algoritmo Knuth Morris Pratt - O(n) Tempo e O(n) Espaço

A idéia básica por trás da abordagem é que calcular o maior substring do final e o comprimento da corda menos esse valor é o mínimo número de anexos. A lógica é intuitiva, não precisamos acrescentar o palíndromo e apenas aqueles que não formam o palíndromo. Para encontrar este maior palíndromo a partir do final, reverter a string calcula o AFD.

O DFA (Autômato Finito Determinístico) mencionado no contexto do Algoritmo Knuth Morris Pratt é um conceito usado para ajudar a encontrar o prefixo mais longo de uma string que também é um sufixo e inverta a string novamente (recuperando assim a string original) e encontre o estado final que representa o número de correspondências da string com a string reverenciada e, portanto, obtemos a maior substring que é um palíndromo do final.

C++
// 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)); 

Saída
2 

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