题目

法1 sort升序排序，再逆序输出

#include<iostream>
#include<algorithm>
using namespace std;

const int N = 5e5+3;//注意const，全局
int a[N];
int main()
{
	//错误int N=5e5+3;
	//错误const int a[N];
	int n;
	cin >> n;
	for (int i = 1; i <= n; ++i)cin >> a[i];
	sort(a + 1, a + n + 1);//从a[1]开始输入，故从a[1]开始排序
	for (int i = 1; i <= n; ++i)cout<< a[i]<<" \n"[i==n];
	//逆序输出
	for (int i = n; i >= 1; --i)cout << a[i] << " \n"[i == 1];
	return 0;
}

“ \n”[i==n]  i=n时回车,其余空格

“ \n”[i==1]  i=1时回车,其余空格

法2 写一个降序cmp函数

#include<iostream>
#include<algorithm>
using namespace std;

const int N = 5e5+3;//注意const，全局
int a[N];

bool cmp(const int& u, const int& v)
{
	return u > v;
}
int main()
{
	//错误int N=5e5+3;
	//错误const int a[N];
	int n;
	cin >> n;
	for (int i = 1; i <= n; ++i)cin >> a[i];
	sort(a + 1, a + n + 1);//从a[1]开始输入，故从a[1]开始排序
	for (int i = 1; i <= n; ++i)cout<< a[i]<<" \n"[i==n];

	sort(a + 1, a + n + 1,cmp);
	for (int i = 1; i <= n; ++i)cout << a[i] << " \n"[i == n];
	return 0;
}