PTA数据结构春季班第一单元_given a sequence a1, a2,..., an, find exactly k di-优快云博客

该博客介绍了如何解决寻找给定整数序列中具有最大和的连续子序列的问题。当所有数字都为负数时，最大子序列和定义为0，并输出整个序列的首尾元素。对于样例输入，序列{-10, 1, 2, 3, 4, -5, -23, 3, 7, -21}的最大子序列和是10，对应的子序列是{1, 2, 3, 4}。" 103032186,275413,Python数据库操作指南：DB-API与SQLite实战,"['数据库', 'Python编程', 'SQLite数据库', '数据库操作']

第一单元习题Maximum Subsequence Sum

Given a sequence of K integers { N1, N2 , …, NK}. A continuous subsequence is defined to be { Ni , Ni+1 , …, Nj } 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

#include <stdio.h>
#include <time.h>
#include <iostream>

struct Result
{
	int Maxsum;
	int StartNum;
	int EndNum;
};

Result MaxSubseqSuml(int A[], int N)
{
	Result ret;

	bool flag = false;		//当前start位置前全是负数
	bool flagfor0 = false;  //当前start位置前全是0
	int NowStartNum = 0;
	int StartNum = 0;
	int EndNum = 0;
	int ThisSum = 0, Maxsum = -1;  //为了在Thissum>Maxsum中不带等于号
	


	for (int i = 0; i < N; i++) {
		ThisSum += A[i];       
		if (flagfor0 && ThisSum >= 0) { //前方是0(或被置为0)且当前和大于等于0
			NowStartNum = i;
			flagfor0 = false;
		}
		
		if (!flag && A[i] >= 0) {  //只要有一个正数flag就一直是true
			flag = true;
		}


		if (ThisSum >Maxsum)
		{
			StartNum = NowStartNum;
			EndNum = i;
			Maxsum = ThisSum;
		}
		if (ThisSum < 0) {
			ThisSum = 0; //abandon the negative subsequence
			flagfor0 = true;
		}

	}

	if (flag) {
		ret.Maxsum = Maxsum;
		ret.StartNum = StartNum;
		ret.EndNum = EndNum;
	}
	else
	{
		ret.Maxsum = 0;
		ret.StartNum = 0;
		ret.EndNum = N-1;
	}

	return ret;
}
int main()
{
	const int MaxSize = 10000;
	int A[MaxSize] = { 0 };
	int K;
	std::cin >> K;
	for (int i = 0; i < K; i++)
		std::cin >> A[i];

	Result res;
	res = MaxSubseqSuml(A, K);

	std::cout << res.Maxsum << " " << A[res.StartNum] << " " << A[res.EndNum];

	system("pause");
	return 0;
}