HDU - 1027 - Ignatius and the Princess II（STL）

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本文介绍了一种利用C++ STL中的next_permutation函数求解特定序列全排列中第M小排列的方法。通过实例演示了如何生成给定范围内数字的所有可能排列，并找出符合要求的特定排列。

Now our hero finds the door to the BEelzebub feng5166. He opens the door and finds feng5166 is about to kill our pretty Princess. But now the BEelzebub has to beat our hero first. feng5166 says, "I have three question for you, if you can work them out, I will release the Princess, or you will be my dinner, too." Ignatius says confidently, "OK, at last, I will save the Princess."

"Now I will show you the first problem." feng5166 says, "Given a sequence of number 1 to N, we define that 1,2,3...N-1,N is the smallest sequence among all the sequence which can be composed with number 1 to N(each number can be and should be use only once in this problem). So it's easy to see the second smallest sequence is 1,2,3...N,N-1. Now I will give you two numbers, N and M. You should tell me the Mth smallest sequence which is composed with number 1 to N. It's easy, isn't is? Hahahahaha......"
Can you help Ignatius to solve this problem?

Input

The input contains several test cases. Each test case consists of two numbers, N and M(1<=N<=1000, 1<=M<=10000). You may assume that there is always a sequence satisfied the BEelzebub's demand. The input is terminated by the end of file.

Output

For each test case, you only have to output the sequence satisfied the BEelzebub's demand. When output a sequence, you should print a space between two numbers, but do not output any spaces after the last number.

Sample Input

6 4
11 8

Sample Output

1 2 3 5 6 4
1 2 3 4 5 6 7 9 8 11 10

此题大意是给出1~n这几个数全排列中第m小的那个排列。求全排列的题可使用STL里的next_permutation不断得到下一个排列，重复m-1次即得到第m个排列。

#include <iostream>
#include <stdio.h>
#include <algorithm>
using namespace std;

int math[1001];

int main() {
	int n,m;
	while(~scanf("%d%d",&n,&m)){
		for(int i=0;i<n;i++)
			math[i]=i+1;	//输入1~n	
		for(int i=1;i<m;i++)
			next_permutation(math,math+n);//STL
		for(int i=0;i<n;i++){
			printf("%d",math[i]);
			if(i==n-1)//注意题目要求的格式：最后一个数后不能输出空格
				printf("\n");
			else
				printf(" ");
		}
	}
	return 0;
}