GukiZ hates Boxes
Professor GukiZ is concerned about making his way to school, because massive piles of boxes are blocking his way.
In total there are n piles of boxes, arranged in a line, from left to right, i-th pile (1 ≤ i ≤ n) containing ai boxes. Luckily, m students are willing to help GukiZ by removing all the boxes from his way. Students are working simultaneously. At time 0, all students are located left of the first pile. It takes one second for every student to move from this position to the first pile, and after that, every student must start performing sequence of two possible operations, each taking one second to complete. Possible operations are:
If i ≠ n, move from pile i to pile i + 1;
If pile located at the position of student is not empty, remove one box from it.
GukiZ's students aren't smart at all, so they need you to tell them how to remove boxes before professor comes (he is very impatient man, and doesn't want to wait). They ask you to calculate minumum time t in seconds for which they can remove all the boxes from GukiZ's way. Note that students can be positioned in any manner after t seconds, but all the boxes must be removed.
Input
The first line contains two integers n and m (1 ≤ n, m ≤ 105), the number of piles of boxes and the number of GukiZ's students.
The second line contains n integers a1, a2, ... an (0 ≤ ai ≤ 109) where ai represents the number of boxes on i-th pile. It's guaranteed that at least one pile of is non-empty.
Output
In a single line, print one number, minimum time needed to remove all the boxes in seconds.
Examples
input
2 1
1 1
output
4
input
3 2
1 0 2
output
5
input
4 100
3 4 5 4
output
5
Note
First sample: Student will first move to the first pile (1 second), then remove box from first pile (1 second), then move to the second pile (1 second) and finally remove the box from second pile (1 second).
Second sample: One of optimal solutions is to send one student to remove a box from the first pile and a box from the third pile, and send another student to remove a box from the third pile. Overall, 5 seconds.
Third sample: With a lot of available students, send three of them to remove boxes from the first pile, four of them to remove boxes from the second pile, five of them to remove boxes from the third pile, and four of them to remove boxes from the fourth pile. Process will be over in 5 seconds, when removing the boxes from the last pile is finished.
题意：有n个空地（1~n），空地上有a[i]块石头，m个学生，每个学生在0这个位置，有两个操作均需要消耗1秒
操作1：将当前所在位置的石头删除
操作2：往右走一个位置，问删除所有空地上的石头需要花费的最少时间
思路：首先可以二分找最优解，在短的时间里可以完成的话，在长的时间里也可以完成。然后就是贪心：找到最后一个非零的位置，计算出到达那里所需的时间，第一个人走到那里之后在剩余的时间里可以把那个位置的石头搬走，或者在剩余的时间里不能够搬完，那么就需要下一个人走到这个地方继续执行和第一个人相同的操作。
#include<queue>
#include<math.h>
#include<vector>
#include<string>
#include<stdio.h>
#include<iostream>
#include<string.h>
#include<algorithm>
#define inf 0x3f3f3f
#define ll long long
#define maxn 110000
using namespace std;
int a[maxn],b[maxn];
int judge(ll t,int n,int m)
{
memcpy(b,a,sizeof(b));//先把a数组的值给b
int p=n;
for(int i=1; i<=m&&p; i++)//m个人
{
while(p&&b[p]==0)p--;
ll l=t-p;
while(p)
{
if(b[p]<=l)
{
l-=b[p];
b[p--]=0;
}
else
{
b[p]-=l;
l=0;
break;
}
}
}
return p==0;//返回能否完成任务
}
int main()
{
int n,m;
ll t=0;
cin>>n>>m;
for(int i=1;i<=n;i++){
cin>>a[i];t+=a[i];}
ll s=1;
t+=(n+1);
while(s<t)//找最优解
{
ll mid=(s+t)/2;
if(judge(mid,n,m))t=mid;
else
s=mid+1;
}
cout<<t<<endl;
}