bzoj3229 石子合并

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxnode 40005
#define LL long long
using namespace std;
int ai[maxnode]={0},t;
LL ans=0;
void work(int x)
{
    int tmp=ai[x]+ai[x-1];ans+=(LL)tmp;int i,j;
    for (i=x;i<t-1;++i) ai[i]=ai[i+1]; --t; 
    for (i=x-1;i&&ai[i-1]<tmp;--i) ai[i]=ai[i-1];
    ai[i]=tmp;
    while(i>=2&&ai[i-2]<=ai[i]){
        j=t-i;work(i-1);i=t-j;
    }
}
int main()
{
    int i,j,n;scanf("%d",&n);
    for (i=0;i<n;++i) scanf("%d",&ai[i]);
    t=1;
    for (i=1;i<n;++i){
        ai[t++]=ai[i];
        while(t>=3&&ai[t-3]<=ai[t-1]) work(t-2);
    }
    while(t>1) work(t-1);
    printf("%I64d\n",ans);
}