HDU3415:Max Sum of Max-K-sub-sequence(单调队列)
2013-07-22 20:14
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[align=left]Problem Description[/align]
Given a circle sequence A[1],A[2],A[3]......A
. Circle sequence means the left neighbour of A[1] is A
, and the right neighbour of A
is A[1].
Now your job is to calculate the max sum of a Max-K-sub-sequence. Max-K-sub-sequence means a continuous non-empty sub-sequence which length not exceed K.
Input
The first line of the input contains an integer T(1<=T<=100) which means the number of test cases.
Then T lines follow, each line starts with two integers N , K(1<=N<=100000 , 1<=K<=N), then N integers followed(all the integers are between -1000 and 1000).
Output
For each test case, you should output a line contains three integers, the Max Sum in the sequence, the start position of the sub-sequence, the end position of the sub-sequence. If there are more than one result, output the minimum start position, if still more than one , output the minimum length of them.
Sample Input
4
6 3
6 -1 2 -6 5 -5
6 4
6 -1 2 -6 5 -5
6 3
-1 2 -6 5 -5 6
6 6
-1 -1 -1 -1 -1 -1
Sample Output
7 1 3
7 1 3
7 6 2
-1 1 1
这是我们集训比赛的一道题,出题人说是什么DP,坑爹啊,比赛完后一看,单调队列,DP还做不出来
然后就果断看了一下单调队列,之是参考别人的代码后才写出来的
单调队列即保持队列中的元素单调递增(或递减)的这样一个队列,可以从两头删除,只能从队尾插入。单调队列的具体作用在于,由于保持队列中的元素满足单调性,对于上述问题中的每个j,可以用O(1)的时间找到对应的s[i]。(保持队列中的元素单调增的话,队首元素便是所要的元素了)。
维护方法:对于每个j,我们插入s[j-1](为什么不是s[j]? 队列里面维护的是区间开始的下标,j是区间结束的下标),插入时从队尾插入。为了保证队列的单调性,我们从队尾开始删除元素,直到队尾元素比当前需要插入的元素优(本题中是值比待插入元素小,位置比待插入元素靠前,不过后面这一个条件可以不考虑),就将当前元素插入到队尾。之所以可以将之前的队列尾部元素全部删除,是因为它们已经不可能成为最优的元素了,因为当前要插入的元素位置比它们靠前,值比它们小。我们要找的,是满足(i>=j-k+1)的i中最小的s[i],位置越大越可能成为后面的j的最优s[i]。
在插入元素后,从队首开始,将不符合限制条件(i>=j-k+1)的元素全部删除,此时队列一定不为空。(因为刚刚插入了一个一定符合条件的元素)
Given a circle sequence A[1],A[2],A[3]......A
. Circle sequence means the left neighbour of A[1] is A
, and the right neighbour of A
is A[1].
Now your job is to calculate the max sum of a Max-K-sub-sequence. Max-K-sub-sequence means a continuous non-empty sub-sequence which length not exceed K.
Input
The first line of the input contains an integer T(1<=T<=100) which means the number of test cases.
Then T lines follow, each line starts with two integers N , K(1<=N<=100000 , 1<=K<=N), then N integers followed(all the integers are between -1000 and 1000).
Output
For each test case, you should output a line contains three integers, the Max Sum in the sequence, the start position of the sub-sequence, the end position of the sub-sequence. If there are more than one result, output the minimum start position, if still more than one , output the minimum length of them.
Sample Input
4
6 3
6 -1 2 -6 5 -5
6 4
6 -1 2 -6 5 -5
6 3
-1 2 -6 5 -5 6
6 6
-1 -1 -1 -1 -1 -1
Sample Output
7 1 3
7 1 3
7 6 2
-1 1 1
这是我们集训比赛的一道题,出题人说是什么DP,坑爹啊,比赛完后一看,单调队列,DP还做不出来
然后就果断看了一下单调队列,之是参考别人的代码后才写出来的
单调队列即保持队列中的元素单调递增(或递减)的这样一个队列,可以从两头删除,只能从队尾插入。单调队列的具体作用在于,由于保持队列中的元素满足单调性,对于上述问题中的每个j,可以用O(1)的时间找到对应的s[i]。(保持队列中的元素单调增的话,队首元素便是所要的元素了)。
维护方法:对于每个j,我们插入s[j-1](为什么不是s[j]? 队列里面维护的是区间开始的下标,j是区间结束的下标),插入时从队尾插入。为了保证队列的单调性,我们从队尾开始删除元素,直到队尾元素比当前需要插入的元素优(本题中是值比待插入元素小,位置比待插入元素靠前,不过后面这一个条件可以不考虑),就将当前元素插入到队尾。之所以可以将之前的队列尾部元素全部删除,是因为它们已经不可能成为最优的元素了,因为当前要插入的元素位置比它们靠前,值比它们小。我们要找的,是满足(i>=j-k+1)的i中最小的s[i],位置越大越可能成为后面的j的最优s[i]。
在插入元素后,从队首开始,将不符合限制条件(i>=j-k+1)的元素全部删除,此时队列一定不为空。(因为刚刚插入了一个一定符合条件的元素)
#include <stdio.h> #include <queue> #include <algorithm> #include <string.h> using namespace std; int a[111111]; int sum[211111]; const int INF = 0x3fffffff; int main() { int t,n,m,i,j,k,head,end; scanf("%d",&t); while(t--) { scanf("%d%d",&n,&k); j = n; sum[0] = 0; for(i = 1; i<=n; i++) { scanf("%d",&a[i]); sum[i] = sum[i-1]+a[i];//将前i项和全部存入sum数组中 } int ans = -INF; for(i = n+1; i<n+k;i++) sum[i] = sum[i-1]+a[i-n]; n = n+k-1; deque<int> Q;//双向队列 Q.clear(); for(i = 1; i<=n; i++) { while(!Q.empty() && sum[i-1]<sum[Q.back()])//保持队列的单调性 Q.pop_back(); while(!Q.empty() && Q.front()<i-k)//超过k的长度则消除队列前面的元素 Q.pop_front(); Q.push_back(i-1); if(sum[i]-sum[Q.front()]>ans)//记录,sum -sum[m]所得出的是n-1到m+1之间的和 { ans = sum[i]-sum[Q.front()]; head = Q.front()+1; end = i; } } if(end>j) end%=j; printf("%d %d %d\n",ans,head,end); } return 0; }
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