PAT甲题题解-1007. Maximum Subsequence Sum (25)-求最大子区间和

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <string.h>
#define INF 0x3f3f3f3f
using namespace std;
const int maxn=10000+5;
int a[maxn];
int maxsum=-INF;
int maxl,maxr;
int l,r;
int main()
{
    int n,val;
    int sum;
    scanf("%d",&n);
    scanf("%d",&a[0]);
    sum=a[0];
    l=0;
    r=0;
    maxl=l;
    maxr=r;
    maxsum=sum;
    bool allnegative=true;
    if(a[0]>=0)
        allnegative=false;
    for(int i=1;i<n;i++){
        scanf("%d",&a[i]);
        if(a[i]>=0)
            allnegative=false;
//printf("l:%d r:%d sum:%d %d:val\n",l,r,sum,a[i]);
        if(sum+a[i]>a[i]){
            sum+=a[i];
            r++;
            if(sum>maxsum){
                maxl=l;
                maxr=r;
                maxsum=sum;
            }
        }
        else{
            sum=a[i];
            l=r=i;
            if(sum>maxsum){
                maxl=l;
                maxr=r;
                maxsum=sum;
            }
        }
    }
    //如果都小于0，按照题目要求，输出0，第一个和最后一个数
    if(allnegative)
        printf("0 %d %d\n",a[0],a[n-1]);
    else
        printf("%d %d %d",maxsum,a[maxl],a[maxr]);
    return 0;
}