1481:Maximum sum

describe

Given a set of n integers: A={a1, a2,…, an}, we define a function d(A) as below:

                 t1     t2      d(A) = max{ ∑ai + ∑aj | 1 <= s1 <= t1 < s2 <= t2 <= n }                i=s1   j=s2

1
2
3
1
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3
Your task is to calculate d(A).

input

The input consists of T(<=30) test cases. The number of test cases (T) is given in the first line of the input.
Each test case contains two lines. The first line is an integer n(2<=n<=50000). The second line contains n integers: a1, a2, …, an. (|ai| <= 10000).There is an empty line after each case.

output

Print exactly one line for each test case. The line should contain the integer d(A).

sample input

1

10
1 -1 2 2 3 -3 4 -4 5 -5
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4
1
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4
sample output

13
1
1
Prompt

In the sample, we choose {2,2,3,-3,4} and {5}, then we can get the answer.

Huge input,scanf is recommended.
这题用两遍dp从左到右算一次，再从右到左算一次。

#include<bits/stdc++.h>using namespace std;int t,n,a[100001],s[100001],r[100001],i,j,minn=-999999,r1[100001];int main(){    cin>>t;    while(t--)    {        cin>>n;        memset(r1,0,sizeof(r1)),memset(a,0,sizeof(a)),memset(s,0,sizeof(s)),memset(r,0,sizeof(r)),minn=-9999999;        for(i=1;i<=n;i++)  cin>>a[i];          s[1]=a[1],r[n]=a[n];          for(i=2;i<=n;i++)             s[i]=max(s[i-1]+a[i],a[i]);             for(i=n-1;i>=1;i--)                    r[i]=max(r[i+1]+a[i],a[i]);                    r1[n]=r[n];                     for(i=n-1;i>=1;i--)                      r1[i]=max(r1[i+1],r[i]);                    for(i=2;i<=n;i++)                       minn=max(minn,s[i-1]+r1[i]);                       cout<<minn<<endl;              }    return 0;}