【POJ】3017 Cut the Sequence

#include<cstdio>
#define MAXN 100010
#define MIN(a,b) ((a)<(b)?(a):(b))
typedef __int64 LL;
LL limit,a[MAXN],dp[MAXN];
int n,Q[MAXN];
LL DoIt()
{
    LL sum;
    int i,j,k,front,rear;
    for(i=1;i<=n;i++)
    {
        if(a[i]>limit)
            return -1;
    }
    sum=dp[0]=0;
    front=0;
    rear=-1;
    for(i=k=1;i<=n;i++)
    {
        sum+=a[i];
        for(;sum>limit;k++)
            sum-=a[k];
        for(;front<=rear&&Q[front]<k;front++);
        for(;front<=rear&&a[Q[rear]]<=a[i];rear--);
        Q[++rear]=i;
        dp[i]=dp[k-1]+a[Q[front]];
        for(j=front;j<rear;j++)
            dp[i]=MIN(dp[i],dp[Q[j]]+a[Q[j+1]]);
    }
    return dp[n];
}
int main()
{
    int i;
    while(~scanf("%d%I64d",&n,&limit))
    {
        for(i=1;i<=n;i++)
            scanf("%I64d",&a[i]);
        printf("%I64d\n",DoIt());
    }
    return 0;
}