PAT (Advanced Level) 1007. Maximum Subsequence Sum (25)

简单DP。

注意：If all the K numbers are negative, then its maximum sum is defined to be 0, and you are supposed to output the first and the last numbers of the whole sequence.

#include<iostream>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<cstdio>
#include<vector>
using namespace std;

const int maxn=10000;
int n,a[maxn],sum,ans1,ans2;
int dp[maxn];

int main()
{
    scanf("%d",&n);
    for(int i=1; i<=n; i++) scanf("%d",&a[i]);
    dp[1]=a[1];
    for(int i=2; i<=n; i++) dp[i]=max(dp[i-1]+a[i],a[i]);
    int Max=-999999999;
    for(int i=1; i<=n; i++) Max=max(Max,dp[i]);
    if(Max<0) printf("0 %d %d
",a[1],a[n]);
    else
    {
        for(int i=1; i<=n; i++)
        {
            if(dp[i]==Max)
            {
                ans2=a[i]; int sum=0;
                for(int j=i; j>=0; j--)
                {
                    sum=sum+a[j];
                    if(sum==Max) { ans1=a[j]; break; }
                }
                break;
            }
        }
        printf("%d %d %d
",Max,ans1,ans2);
    }
    return 0;
}