练习1

Description

The Little Elephant enjoys recursive functions.

This time he enjoys the sorting function. Let a is a permutation of an integers from 1 to n, inclusive, and a_i denotes the i-th element of the permutation. The Little Elephant's recursive function f(x), that sorts the first x permutation's elements, works as follows:

• If x = 1, exit the function.
• Otherwise, call f(x - 1), and then make swap(a_x - 1, a_x) (swap the x-th and (x - 1)-th elements of a).

The Little Elephant's teacher believes that this function does not work correctly. But that-be do not get an F, the Little Elephant wants to show the performance of its function. Help him, find a permutation of numbers from 1 to n, such that after performing the Little Elephant's function (that is call f(n)), the permutation will be sorted in ascending order.

#include<iostream>using namespace std;int a[1005];//此处递归的结构究竟是什么 void f(int n){if(n==1) return;else{f(n-1);swap(a[n-2],a[n-1]);//递归调用的本质。注意每次是按顺序执行，执行完f(n-1)才是swap语句 }}int main(){int n;cin>>n;if(n==1) cout<<n<<endl;else if(n==2)cout<<2<<" "<<1<<endl;else{cout<<n<<" ";a[0]=n;for(int i=1;i<=n-1;i++){cout<<i<<" ";a[i]=i;}}cout<<endl;f(n);for(int i=0;i<n;i++)cout<<a[i]<<" ";}