编写程序以打印给定字符串的所有排列

排列(也称为“排列编号”或“顺序”)是将有序列表S的元素重新排列为与S本身一一对应的关系。长度为n的字符串为n！排列。

资料来源：Mathword(http://mathworld.wolfram.com/Permutation.html)

以下是字符串ABC的排列。
ABC ACB BAC BCA CBA CAB

这是用作回溯基础的解决方案。

C++

// C++ program to print all
// permutations with duplicates allowed
#include 
using namespace std;
 
 
// Function to print permutations of string
// This function takes three parameters:
// 1. String
// 2. Starting index of the string
// 3. Ending index of the string.
void permute(string a, int l, int r)
{
    // Base case
    if (l == r)
        cout<

---

C

// C program to print all permutations with duplicates allowed
#include 
#include 
 
/* Function to swap values at two pointers */
void swap(char *x, char *y)
{
    char temp;
    temp = *x;
    *x = *y;
    *y = temp;
}
 
/* Function to print permutations of string
This function takes three parameters:
1. String
2. Starting index of the string
3. Ending index of the string. */
void permute(char *a, int l, int r)
{
int i;
if (l == r)
    printf("%s\n", a);
else
{
    for (i = l; i <= r; i++)
    {
        swap((a+l), (a+i));
        permute(a, l+1, r);
        swap((a+l), (a+i)); //backtrack
    }
}
}
 
/* Driver program to test above functions */
int main()
{
    char str[] = "ABC";
    int n = strlen(str);
    permute(str, 0, n-1);
    return 0;
}

Java

// Java program to print all permutations of a
// given string.
public class Permutation
{
    public static void main(String[] args)
    {
        String str = "ABC";
        int n = str.length();
        Permutation permutation = new Permutation();
        permutation.permute(str, 0, n-1);
    }
 
    /**
    * permutation function
    * @param str string to calculate permutation for
    * @param l starting index
    * @param r end index
    */
    private void permute(String str, int l, int r)
    {
        if (l == r)
            System.out.println(str);
        else
        {
            for (int i = l; i <= r; i++)
            {
                str = swap(str,l,i);
                permute(str, l+1, r);
                str = swap(str,l,i);
            }
        }
    }
 
    /**
    * Swap Characters at position
    * @param a string value
    * @param i position 1
    * @param j position 2
    * @return swapped string
    */
    public String swap(String a, int i, int j)
    {
        char temp;
        char[] charArray = a.toCharArray();
        temp = charArray[i] ;
        charArray[i] = charArray[j];
        charArray[j] = temp;
        return String.valueOf(charArray);
    }
 
}
 
// This code is contributed by Mihir Joshi

Python

# Python program to print all permutations with
# duplicates allowed
 
def toString(List):
    return ''.join(List)
 
# Function to print permutations of string
# This function takes three parameters:
# 1. String
# 2. Starting index of the string
# 3. Ending index of the string.
def permute(a, l, r):
    if l==r:
        print toString(a)
    else:
        for i in xrange(l,r+1):
            a[l], a[i] = a[i], a[l]
            permute(a, l+1, r)
            a[l], a[i] = a[i], a[l] # backtrack
 
# Driver program to test the above function
string = "ABC"
n = len(string)
a = list(string)
permute(a, 0, n-1)
 
# This code is contributed by Bhavya Jain

C#

// C# program to print all
// permutations of a given string.
using System;
 
class GFG
{
    /**
    * permutation function
    * @param str string to
    calculate permutation for
    * @param l starting index
    * @param r end index
    */
    private static void permute(String str,
                                int l, int r)
    {
        if (l == r)
            Console.WriteLine(str);
        else
        {
            for (int i = l; i <= r; i++)
            {
                str = swap(str, l, i);
                permute(str, l + 1, r);
                str = swap(str, l, i);
            }
        }
    }
 
    /**
    * Swap Characters at position
    * @param a string value
    * @param i position 1
    * @param j position 2
    * @return swapped string
    */
    public static String swap(String a,
                            int i, int j)
    {
        char temp;
        char[] charArray = a.ToCharArray();
        temp = charArray[i] ;
        charArray[i] = charArray[j];
        charArray[j] = temp;
        string s = new string(charArray);
        return s;
    }
 
// Driver Code
public static void Main()
{
    String str = "ABC";
    int n = str.Length;
    permute(str, 0, n-1);
}
}
 
// This code is contributed by mits

输出：

ABC
ACB
BAC
BCA
CBA
CAB

算法范例：回溯

时间复杂度： O(n * n！)注意，这里有n！排列，并且需要O(n)时间才能打印一个排列。

注意：如果输入字符串有重复的字符，则上述解决方案将打印重复的排列。请参阅下面的链接以获取一种解决方案，即使输入中存在重复项，该解决方案也仅打印不同的排列。
打印重复的给定字符串的所有不同排列。
使用STL对给定的字符串进行排列

另一种方法：

C++

#include 
#include 
using namespace std;
 
void permute(string s , string answer)
{
    if(s.length() == 0)
    {
        cout<>s;
 
    cout<<"\nAll possible strings are : ";
    permute(s , answer);
    return 0;
}

Output:
Enter the string : abc
All possible strings are : abc  acb  bac  bca  cab  cba