Algorithm1: 全排列

全排列

思想：

     这是一个全排列问题，需要使用递归实现，将数组中的所有元素和第一个元素交换，求后面n-1个元素的全排列。

     按照这个条件递归下去，知道元素的个数只有一个的时候，输出所有的元素。

 

#include <iostream>

using namespace std;

 

int total = 0;

void perm(int arr[], int start , int size){

                 if (start >= size){

                                 for (int i = 0; i < size; i++){

                                                cout << arr[i] << " " ;

                                }

                                cout << endl;

                                total++;

                                 //return;

                }

                 else{

                                 for (int i = start; i < size; i++){

                                                 int temp = arr [start];

                                                 arr[start ] = arr[i];

                                                 arr[i] = temp;

 

                                                perm( arr, start + 1, size);

 

                                                temp = arr[start ];

                                                 arr[start ] = arr[i];

                                                 arr[i] = temp;

                                }

                }

}

 

int main(){

                 int a [] = { 1, 2, 3, 4, 5, 6 };

                perm(a, 0, 3);

                cout<< total << endl;

                 return 0;

}

 

此外在C++STL中也有一个关于全排列的函数：

     next_permuntation(start, start_length);

     int a [] = { 1, 2, 3, 4, 5, 6 };

                sort(a, a + 6);

                 while (next_permutation(a, a + 6)){

                                 for (int i = 0; i < 6; i++){

                                                cout << a[i] << " " ;

                                }

                                cout << endl;

                }