题目:
https://www.luogu.org/problem/show?pid=1094
闲着没事逛洛谷,发现了这个一年前留的坑,顺手填了;
一年以来第一次手打排序……
#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
const int MAXN=100001;
int d,n,ans;
int a[MAXN],s[MAXN];
queue<int>q;
void merge_sort(int l,int r)
{
if(l==r) return;
int mid=(l+r)>>1;
merge_sort(l,mid),merge_sort(mid+1,r);
int i=l,k=l,j=mid+1;
while(i<=mid && j<=r)
if(a[i]>a[j]) s[k++]=a[j++];
else s[k++]=a[i++];
while(i<=mid) s[k++]=a[i++];
while(j<=r) s[k++]=a[j++];
for(int i=l;i<=r;i++) a[i]=s[i];
return;
}
void solve()
{
scanf("%d%d",&d,&n);
for(int i=1;i<=n;i++) scanf("%d",&a[i]);
merge_sort(1,n);
int l=1,r=n;
while(l<=r)
{
if(a[l]+a[r]<=d) ans++,r--,l++;
else r--,ans++;
}
cout<<ans;
}
int main()
{
solve();
return 0;
}