BZOJ 2151 种树

贪心+priority_queue。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
#define maxn 200050
using namespace std;
long long n,val[maxn],ans=0,m;
bool vis[maxn];
struct node
{
    long long w,pos;
    friend bool operator < (node x,node y)
    {
        return x.w<y.w;
    }
};
priority_queue <node> q;
int main()
{
    memset(vis,true,sizeof(vis));
    scanf("%lld%lld",&n,&m);
    for (long long i=0;i<n;i++)
    {
        scanf("%lld",&val[i]);
        node now;
        now.w=val[i];now.pos=i;
        q.push(now);
    }
    if (m>=(n/2)+1) {printf("Error!\n");return 0;}
    long long cnt=0;
    do
    {
        node now=q.top();
        q.pop();
        if (vis[now.pos]==true)
        {
            cnt++;
            long long left=(now.pos-1+n)%n,right=(now.pos+1+n)%n;
            while (vis[left]==false) 
                left=(left-1+n)%n;
            while (vis[right]==false)
            right=(right+1+n)%n;
            vis[left]=false;vis[right]=false;
            node then;
            then.w=val[left]+val[right]-val[now.pos];
            then.pos=now.pos;
            q.push(then);
            ans=ans+val[now.pos];
            val[now.pos]=val[left]+val[right]-val[now.pos];
        }
    }while (cnt!=m);
    printf("%lld\n",ans);
    return 0;
}