PAT 1007 Maximum Subsequence Sum (25分)

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Meaning: Given a $For$ a sequence of$K$ integers, the largest subsequence refers to the largest sum of all elements in the continuous subsequence. For example, given the sequence{− 2, 11, − 4, 13, − 5, − 2} \left\{-2, 11, -4, 13, -5, -2\right\}{ −2,11,−4,13,−5,− 2 } , the largest subsequence is{11, − 4, 13} \left\{11, -4, 13\right\}{ 11,−4,1 3 } , the maximum sum is$20$ . Now you need to find the largest sum, and the first and last numbers of the largest subsequence.

Ideas:

A detailed explanation about the maximum subsequence sum: click here

On the basis of the above code, how to find the first and last numbers of the largest subsequence?

Since the subsequences we are looking for are all disjoint, so in the variable $s$ clear$When\; 0$ , record the first number of the largest subsequence$start$ ; when updating the answer, record the last number of the largest subsequence$r$ , updatellat the same time$l$。

AC code:

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>

using namespace std;
const int N = 10010;

int a[N];

int main()
{
    
    
    int n, x;
    scanf("%d", &n);
    for(int i = 0; i < n; i++)  scanf("%d", &a[i]);
    
    int ans = -1e9, s = 0;
    int start = 0, l, r;
    for(int i = 0; i < n; i++)
    {
    
    
        if(s < 0)
        {
    
    
            s = 0;
            start = i;
        }
        s += a[i];
        if(s > ans)
        {
    
    
            ans = s;
            l = start, r = i;
        }
    }
    
    if(ans < 0) ans = 0, l = 0, r = n - 1;
    
    printf("%d %d %d", ans, a[l], a[r]);
    
    return 0;
}

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