全排列（總結）

按字典序進行全排列

1.對1~n進行全排列（遞歸）

#include<stdio.h>
int a[6];
int visited[6];
int n;

void dfs(int position)
{
	if(position == n+1)
	{
		for(int i = 1;i <= n;i ++)
		printf("%d",a[i]);
		printf("\n");
		return;
	}
	for(int i = 1;i <= n;i ++)
	{
		if(!visited[i])
		{
			a[position] = i;
			visited[i] = 1;
			dfs(position+1);
			visited[i] = 0;
		}
	}
}

int main()
{
	scanf("%d",&n);
	dfs(1);
	return 0;
}

2.對n個不相同的數進行全排列

#include<stdio.h>
int A[] = {2,5,9};//對A進行全排列 
int B[3];//存放全排列
int n = 3;//數組長度 

void print_permutation(int position) 
{
	if(position == n) 
	{
		for(int i = 0;i < n;i ++)
		printf("%d",B[i]);
		printf("\n");
		return;
	}
	for(int i = 0;i < n;i ++)
	{
		int ok = 1;
		for(int j = 0;j < position;j ++)
		if(B[j] == A[i])
		{
			ok = 0;
			break;
		}
		if(ok)
		{
			B[position] = A[i];
			print_permutation(position+1);
		}
	}
}

int main()
{
	print_permutation(0);
	return 0;
}

3.對n個有重複的數進行排列

#include<stdio.h>
int A[] = {2,7,7};//對A進行全排列 
int B[3];//對每次排列的記錄 
int n = 3;//排列數組的長度

void print_permutation(int position) 
{
	if(position == n)
	{
		for(int i = 0;i < n;i ++)
		printf("%d",B[i]);
		printf("\n");
		return;
	}
	for(int i = 0;i < n;i ++)
	if(!i || A[i] != A[i-1])
	{
		int c1 = 0;
		int c2 = 0;
		for(int j = 0;j < position;j ++)
		if(A[i] == B[j]) c1 ++;
		for(int j = 0;j < n;j ++)
		if(A[i] == A[j]) c2 ++;
		if(c1 < c2)
		{
			B[position] = A[i];
			print_permutation(position+1);
		}
	}
}

int main()
{
	print_permutation(0);
	return 0;
}