求最大子序列和的问题

Question

问题遇到的现象和发生背景 2004浙大考研复试题，求最大子序列和，若相等则输出更前面的，若为负数则令其为0

原题：
Given a sequence of K integers { N1，N2，……，NK
}. A continuous subsequence is defined to be { N
i, N i+1, ……, N j} where 1≤i≤j≤K. The Maximum Subsequence is the continuous subsequence which has the largest sum of its elements. For example, given sequence { -2, 11, -4, 13, -5, -2 }, its maximum subsequence is { 11, -4, 13 } with the largest sum being 20.

Now you are supposed to find the largest sum, together with the first and the last numbers of the maximum subsequence.

Input Specification:
Each input file contains one test case. Each case occupies two lines. The first line contains a positive integer K (≤10000). The second line contains K numbers, separated by a space.

Output Specification:
For each test case, output in one line the largest sum, together with the first and the last numbers of the maximum subsequence. The numbers must be separated by one space, but there must be no extra space at the end of a line. In case that the maximum subsequence is not unique, output the one with the smallest indices i and j (as shown by the sample case). 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.

问题相关代码，请勿粘贴截图

#include<stdio.h>
int main()
{
    int n,i,sum=0,a[100000],max=0,flag,start,end;
    scanf("%d",&n);
    for(i=0;i<n;i++){scanf("%d",&a[i]);
         if(sum==0&&a[i]>0)flag=i;
         sum=sum+a[i];
         if(sum>max){
             start=flag;
             max=sum;
             end=i;
         }
         if(sum<0)sum=0;
         if(max==0)start=end=0;
}
    printf("%d %d %d",max,a[start],a[end]);
    return 0;
}

运行结果及报错内容 部分正确，在“全是负数”“负数和0”“最大和前面有一段是0”这三项一直都挂了

我的解答思路和尝试过的方法 对于全是负数，在循环最后加了if{max==0}语句输出特殊情况；对于最大和前面有一段是0，在循环前面只有sum初始或被更新后且元素大于0才记录

Answer 1

• 你看下这篇博客吧, 应该有用👉 ：最大连续子序列和