字符串全排列【方法2：利用交换的思想】

//方法2：利用交换的思想，具体见实例，但该方法不如方法1容易理解。
//
//?
#include <iostream>
#include <string>
#include <cstdio>
using namespace std;
 
void swap(char* x, char* y)
{
	if(x==y)
		return;
    char tmp;
    tmp = *x;
    *x = *y;
    *y = tmp;
}
 
/* 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 i, int n)
{
   int j;
   if (i == n)
     printf("%s\n", a);
   else
   {
        for (j = i; j <= n; j++)
       {
          if(a[i] == a[j] && j != i)  //为避免生成重复排列，当不同位置的字符相同时不再交换
			continue;
          swap((a+i), (a+j));//a[i]<->a[j]
          permute(a, i+1, n);
          swap((a+i), (a+j)); //backtrack//a[i]<->a[j]
       }
   }
} 

void permute_my(char *a, int i, int n)
{
   int j;
   if (i == n)
     printf("%s\n", a);
   else
   {
        for (j = i; j <= n; j++)
       {
          if(a[i] == a[j] && j != i)  //为避免生成重复排列，当不同位置的字符相同时不再交换
			continue;
          //swap((a+i), (a+j));//a[i]<->a[j]
		  char buff[256];
		  strcpy(buff,a);
		  swap(&buff[i],&buff[j]);//buff[i]<->buff[j]
		  
          permute_my(buff, i+1, n);
          //swap((a+i), (a+j)); //backtrack//a[i]<->a[j]
       }
   }
} 
 
int main()
{
    //method2
    cout << "method2" << endl;
    char a[] = "ABA";
    permute(a,0,strlen(a)-1);
	///////
	printf("==========\n");
    char b[] = "ABA";
    permute_my(b,0,strlen(b)-1);
    return 0;
}