1007 Maximum Subsequence Sum (25 分)（有坑，最大子段和）

https://pintia.cn/problem-sets/994805342720868352/problems/994805514284679168

Given a sequence of K integers { N​1​​, N​2​​, ..., N​K​​ }. 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.

Sample Input:

10 -10 1 2 3 4 -5 -23 3 7 -21

Sample Output:

10 1 4

 

 输出最大子段和以及它两端的数

当最大子段和不唯一时输出最靠左的

思路：设初始ans为一个负数，这样当序列中有非负数的时候,那么ans一定会被更新变为非负数

如果最后ans是负数，那么序列中一定全是负数，按照题意输出即可

#include<bits/stdc++.h> #pragma GCC optimize(3) #define max(a,b) a>b?a:b using namespace std; typedef long long ll; int a[10005]; int main(){ int n; cin>>n; for(int i=1;i<=n;i++) cin>>a[i]; ll ans=-1; ll cnt=0; int L=1,R=n,l=1,r=1; for(int i=1;i<=n;i++){ r=i; cnt+=a[i]; if(cnt>ans){ L=l,R=r; ans=cnt; } if(cnt<0){ cnt=0; l=i+1; r=i+1; } } if(ans<0) cout<<0<<" "<<a[1]<<" "<<a[n]<<endl; else cout<<ans<<" "<<a[L]<<" "<<a[R]<<"\n"; return 0; }