通过改变大小写来替换字符串

打印一个字符串的所有排列，保留序列但改变大小写。

例子：

Input : ab
Output : AB Ab ab aB

Input : ABC
Output : abc Abc aBc ABc abC AbC aBC ABC

方法1(天真)：天真的方法是遍历整个字符串，对于每个字符，请考虑两种情况：(1)改变大小写和重复(2)不要改变大小写和重复。

方法2(更好)对于长度为n的字符串，存在2 ^n个最大组合。我们可以将其表示为按位运算。
在“打印所有子序列”中讨论了相同的想法。

下面是上述想法的实现：

C++

// CPP code to print all permutations
// with respect to cases
#include 
using namespace std;
  
// Function to generate permutations
void permute(string input)
{
    int n = input.length();
  
    // Number of permutations is 2^n
    int max = 1 << n;
  
    // Converting string to lower case
        transform(input.begin(), input.end(), input.begin(), 
                                                ::tolower);
    // Using all subsequences and permuting them
    for (int i = 0; i < max; i++) {
          
        // If j-th bit is set, we convert it to upper case
        string combination = input;
        for (int j = 0; j < n; j++) 
            if (((i >> j) & 1) == 1)
                combination[j] = toupper(input.at(j));     
  
        // Printing current combination
        cout << combination << " ";
    }
}
  
// Driver code
int main()
{
    permute("ABC");
    return 0;
}

Java

// Java program to print all permutations
// with respect to cases
  
public class PermuteString 
{
    // Function to generate permutations
    static void permute(String input)
    {
        int n = input.length();
          
        // Number of permutations is 2^n
        int max = 1 << n;
          
        // Converting string to lower case
        input = input.toLowerCase();
          
        // Using all subsequences and permuting them
        for(int i = 0;i < max; i++)
        {
            char combination[] = input.toCharArray();
              
            // If j-th bit is set, we convert it to upper case
            for(int j = 0; j < n; j++)
            {
                if(((i >> j) &  1) == 1)
                    combination[j] = (char) (combination[j]-32);
            }
              
            // Printing current combination
            System.out.print(combination);
            System.out.print("   ");
        }
    }
      
    // Driver Program to test above function
    public static void main(String[] args) 
    {
        permute("ABC");
    }
}
  
// This code is contributed by Sumit Ghosh

Python

# Python code to print all permutations
# with respect to cases
  
# Function to generate permutations
def permute(inp):
    n = len(inp)
   
    # Number of permutations is 2^n
    mx = 1 << n
   
    # Converting string to lower case
    inp = inp.lower()
      
    # Using all subsequences and permuting them
    for i in range(mx):
        # If j-th bit is set, we convert it to upper case
        combination = [k for k in inp]
        for j in range(n):
            if (((i >> j) & 1) == 1):
                combination[j] = inp[j].upper()
   
        temp = ""
        # Printing current combination
        for i in combination:
            temp += i
        print temp, 
          
# Driver code
permute("ABC")
  
# This code is contributed by Sachin Bisht

C#

// C# program to print all permutations
// with respect to cases
using System;
  
class PermuteString  {
      
    // Function to generate 
    // permutations
    static void permute(String input)
    {
        int n = input.Length;
          
        // Number of permutations is 2^n
        int max = 1 << n;
          
        // Converting string
        // to lower case
        input = input.ToLower();
          
        // Using all subsequences 
        // and permuting them
        for(int i = 0;i < max; i++)
        {
            char []combination = input.ToCharArray();
              
            // If j-th bit is set, we 
            // convert it to upper case
            for(int j = 0; j < n; j++)
            {
                if(((i >> j) & 1) == 1)
                    combination[j] = (char) (combination[j] - 32);
            }
              
            // Printing current combination
            Console.Write(combination);
            Console.Write(" ");
        }
    }
      
    // Driver Code
    public static void Main() 
    {
        permute("ABC");
    }
}
  
// This code is contributed by Nitin Mittal.

PHP

> $j) & 1) == 1)
                $combination[$j] = chr(ord($combination[$j]) - 32);
        }
          
        // Printing current combination
        echo $combination . " ";
    }
}
  
// Driver Code
permute("ABC");
  
// This code is contributed by mits
?>

输出：

abc Abc aBc ABc abC AbC aBC ABC

询问：Facebook。