根据给定的条件从给定的字符串 P 和 Q 生成一个字符串

给定两个字符串P和Q，任务是生成满足以下条件的字符串S ：

• 找到S使得P被重新排列并且Q是其中的一个子串。
• S 中Q之前的所有字符应小于或等于Q 中的第一个字符，并按字典顺序排列。
• 其余字符应按字典顺序出现在Q之后

注意： Q 的所有字符总是出现在 P 中，并且 Q 的长度总是小于或等于 P 的长度。

例子：

Input : P = “geeksforgeeksfor” Q = “for”
Output : eeeefforggkkorss
Explanation: 
The characters ‘e’ and ‘f’ are the only characters here which are less than or equal to ‘f’ (first character of Q). 
So, before “for” the string is lexicographically equal to eeeef. 
The rest of the characters in P are greater than ‘f’, so they are placed after “for” in lexicographic order. 
Thus, after “for”, the string is ggkkorss. 
Therefore the output is eeeefforggkkorss.

Input : P = “lexicographical” Q = “gap”
Output : accegaphiillorx
Explanation: 
The string accegaphiillorx satisfies the above conditions for string P and Q.

方法：这个想法是找到 P 和 Q 中所有字符的频率来解决问题。

• 维护 P 和 Q 中所有字母的频率数组。
• 找到频率后，根据在Q中的第一个字符P中分离字符，并将它们添加到所得到的字符串。
• 最后返回结果字符串。

下面是上述方法的实现：

C++

// C++ program to implement
// the above approach
#include 
using namespace std;
 
// Function to generate a string S from string P
// and Q according to the given conditions
void manipulateStrings(string P, string Q)
{
 
    // Stores the frequencies
    int freq[26];
    memset(freq, 0, sizeof(freq));
     
    // Counts occurrences of each characters
    for(int i = 0; i < P.size(); i++)
    {
        freq[P[i] - 'a']++;
    }
 
    // Reduce the count of the character
    // which is also present in Q
    for(int i = 0; i < Q.size(); i++)
    {
        freq[Q[i] - 'a']--;
    }
 
    // Stores the resultant string
    string sb = "";
 
    // Index in freq[] to segregate the string
    int pos = Q[0] - 'a';
 
    for(int i = 0; i <= pos; i++)
    {
        while (freq[i] > 0)
        {
            char c = (char)('a' + i);
            sb += c;
            freq[i]--;
        }
    }
 
    // Add Q to the resulting string
    sb += Q;
 
    for(int i = pos + 1; i < 26; i++)
    {
        while (freq[i] > 0)
        {
            char c = (char)('a' + i);
            sb += c;
            freq[i]--;
        }
    }
 
    cout << sb << endl;
}
 
// Driver Code
int main()
{
    string P = "geeksforgeeksfor";
    string Q = "for";
     
    // Function call
    manipulateStrings(P, Q);
}
 
// This code is contributed by Amit Katiyar

Java

// Java Program to implement
// the above approach
import java.util.*;
import java.lang.*;
import java.io.*;
 
class GFG {
 
    // Function to generate a string S from string P
    // and Q according to the given conditions
    public static void manipulateStrings(String P,
                                         String Q)
    {
 
        // Stores the frequencies
        int[] freq = new int[26];
 
        // Counts occurrences of each characters
        for (int i = 0; i < P.length(); i++) {
            freq[P.charAt(i) - 'a']++;
        }
 
        // Reduce the count of the character
        // which is also present in Q
        for (int i = 0; i < Q.length(); i++) {
            freq[Q.charAt(i) - 'a']--;
        }
 
        // Stores the resultant string
        StringBuilder sb
            = new StringBuilder();
 
        // Index in freq[] to segregate the string
        int pos = Q.charAt(0) - 'a';
 
        for (int i = 0; i <= pos; i++) {
            while (freq[i] > 0) {
                char c = (char)('a' + i);
                sb.append(c);
                freq[i]--;
            }
        }
 
        // Add Q to the resulting string
        sb.append(Q);
 
        for (int i = pos + 1; i < 26; i++) {
            while (freq[i] > 0) {
                char c = (char)('a' + i);
                sb.append(c);
                freq[i]--;
            }
        }
 
        System.out.println(sb);
    }
 
    // Driver Code
    public static void main(String[] args)
    {
        String P = "geeksforgeeksfor";
        String Q = "for";
        // Function call
        manipulateStrings(P, Q);
    }
}

Python3

# Python3 program to implement
# the above approach
 
# Function to generate a string S
# from string P and Q according to
# the given conditions
def manipulateStrings(P, Q):
  
    # Stores the frequencies
    freq = [0 for i in range(26)];
      
    # Counts occurrences of each characters
    for i in range(len(P)):
        freq[ord(P[i]) - ord('a')] += 1
  
    # Reduce the count of the character
    # which is also present in Q
    for i in range(len(Q)):
        freq[ord(Q[i]) - ord('a')] -= 1
  
    # Stores the resultant string
    sb = ""
  
    # Index in freq[] to segregate the string
    pos = ord(Q[0]) - ord('a')
     
    for i in range(pos + 1):
        while freq[i] > 0:
            sb += chr(ord('a') + i)
            freq[i] -= 1
  
    # Add Q to the resulting string
    sb += Q
     
    for i in range(pos + 1, 26):
        while freq[i] > 0:
            sb += chr(ord('a') + i)
            freq[i] -= 1
     
    print(sb)
     
# Driver Code
if __name__=="__main__":
     
    P = "geeksforgeeksfor";
    Q = "for";
      
    # Function call
    manipulateStrings(P, Q);
 
# This code is contributed by rutvik_56

C#

// C# Program to implement
// the above approach
using System;
class GFG{
 
  // Function to generate a string S from string P
  // and Q according to the given conditions
  public static void manipulateStrings(String P,
                                       String Q)
  {
 
    // Stores the frequencies
    int[] freq = new int[26];
 
    // Counts occurrences of each characters
    for (int i = 0; i < P.Length; i++)
    {
      freq[P[i] - 'a']++;
    }
 
    // Reduce the count of the character
    // which is also present in Q
    for (int i = 0; i < Q.Length; i++)
    {
      freq[Q[i] - 'a']--;
    }
 
    // Stores the resultant string
    String sb = "";
 
    // Index in []freq to segregate the string
    int pos = Q[0] - 'a';
 
    for (int i = 0; i <= pos; i++)
    {
      while (freq[i] > 0)
      {
        char c = (char)('a' + i);
        sb += c;
        freq[i]--;
      }
    }
 
    // Add Q to the resulting string
    sb += Q;
 
    for (int i = pos + 1; i < 26; i++)
    {
      while (freq[i] > 0)
      {
        char c = (char)('a' + i);
        sb += c;
        freq[i]--;
      }
    }
    Console.WriteLine(sb);
  }
 
  // Driver Code
  public static void Main(String[] args)
  {
    String P = "geeksforgeeksfor";
    String Q = "for";
     
    // Function call
    manipulateStrings(P, Q);
  }
}
 
// This code is contributed by Rohit_ranjan

Javascript

 
      // JavaScript Program to implement
      // the above approach
       
      // Function to generate a string S from string P
      // and Q according to the given conditions
      function manipulateStrings(P, Q) {
        // Stores the frequencies
        var freq = new Array(26).fill(0);
 
        // Counts occurrences of each characters
        for (var i = 0; i < P.length; i++) {
          freq[P[i].charCodeAt(0) - "a".charCodeAt(0)]++;
        }
 
        // Reduce the count of the character
        // which is also present in Q
        for (var i = 0; i < Q.length; i++) {
          freq[Q[i].charCodeAt(0) - "a".charCodeAt(0)]--;
        }
 
        // Stores the resultant string
        var sb = "";
 
        // Index in []freq to segregate the string
        var pos = Q[0].charCodeAt(0) - "a".charCodeAt(0);
 
        for (var i = 0; i <= pos; i++) {
          while (freq[i] > 0) {
            var c = String.fromCharCode("a".charCodeAt(0) + i);
            sb += c;
            freq[i]--;
          }
        }
 
        // Add Q to the resulting string
        sb += Q;
 
        for (var i = pos + 1; i < 26; i++) {
          while (freq[i] > 0) {
            var c = String.fromCharCode("a".charCodeAt(0) + i);
            sb += c;
            freq[i]--;
          }
        }
        document.write(sb);
      }
 
      // Driver Code
      var P = "geeksforgeeksfor";
      var Q = "for";
 
      // Function call
      manipulateStrings(P, Q);
       

输出：

eeeefforggkkorss

时间复杂度： O(N+M)，其中 N 和 M 分别是 P 和 Q 的长度。
辅助空间： O(1)

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