一、題目：

01-複雜度2 Maximum Subsequence Sum （25 分）

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

作者: 陳越

單位: 浙江大學

時間限制: 200 ms

記憶體限制: 64 MB

二、程式碼

本人程式碼並沒有拿到測試滿分（25），只拿到23分，測試點2並列和對應相同i但是不同j，即尾是0這個測試點沒有通過。我一直沒有找到例子和程式碼的錯誤，希望看懂的發我測試樣例，後期更新

#include<iostream>
using namespace std;
void MaxSubsequenceSum(int A[],int N)
{
	int flag = 0;  //flag標誌量 
	int ThisSum = 0, MaxSum = 0;  //當前和，序列最大和 
	int start = 0, end = 0,count = 0;   //保留起點和終點 
	for(int i = 0;i < N; i++)     //判斷全是負數 
	{	
		if(A[i] < 0)
			count++;
		if(count == N)
		{
			cout <<0<<" "<<A[0]<<" "<<A[N-1];
			return;
		}
	}    
	//線上處理演算法 
	for(int i = 0;i < N; i++)
	{
		ThisSum = ThisSum + A[i]; 
		if(ThisSum < 0)
		{
			ThisSum = 0;
			if(!flag)             // 這個標誌量主要用於start,標誌是否丟棄前面ThisSum 
				flag = 1;
			if(A[i + 1] == 0)    //判斷當前ThisSum<0並且下一個數為零的情況，對start和end更新 
				{
					flag = 0;
					end = start = i + 1;	
					
				}	
		}
		if(ThisSum > MaxSum)
		{
			if(flag)
			start = i;
			MaxSum = ThisSum;
			end = i;
			flag = 0;		//每次更新完start、end後，重置標誌變數 
		}
	}
		cout<<MaxSum<<" "<<A[start]<<" "<<A[end];
}
int main()
{
		int n;
		cin>>n;
		int *A = new int[n];
		for(int i = 0;i < n;i++)
			cin>>A[i];
		MaxSubsequenceSum(A,n); 
}