题解 | #[NOIP2007]纪念品分组#双指针

#include<bits/stdc++.h>
#define io ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
using namespace std;
typedef long long int ll;
typedef pair<int,int> PII;
#define int long long

int w,n;
const int N = 1e5+10;
int a[N];
int ans;
signed main()
{
    io;
    cin>>w>>n;
    for(int i=1;i<=n;i++)cin>>a[i];
    
    sort(a+1,a+1+n);
    int l=1,r=n;
    while(l<=r)
    {
        if(a[l]+a[r] <= w)
        {
            l++,r--;
            ans++;
        }
        else
        {
            if(a[r] <= w)
            {
                ans++;
            }
            r--;
        }
    }
    cout<<ans<<endl;
    return 0;
}