#C++初学记录(ACM试题2）

Max Sum **

Given a sequence a[1],a[2],a[3]......a[n], your job is to calculate the max sum of a sub-sequence. For example, given (6,-1,5,4,-7), the max sum in this sequence is 6 + (-1) + 5 + 4 = 14.

Input**

The first line of the input contains an integer T(1<=T<=20) which means the number of test cases. Then T lines follow, each line starts with a number N(1<=N<=100000), then N integers followed(all the integers are between -1000 and 1000).

Output

For each test case, you should output two lines. The first line is "Case #:", # means the number of the test case. The second line contains three integers, the Max Sum in the sequence, the start position of the sub-sequence, the end position of the sub-sequence. If there are more than one result, output the first one. Output a blank line between two cases.

Sample Input

2

5 6 -1 5 4 -7

7 0 6 -1 1 -6 7 -5

Sample Output

Case 1:

14 1 4

Case 2:

7 1 6

正确代码

#include<iostream>
#include<cstdio>
using namespace std;
int a[200];
int main()
{
	int n;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		int t,resmax=0,sursum=0,curleft=1,temp=0,resleft=0,resright,ressum=0;
		cin>>t;
		for(int i=1;i<=t;i++)
		{
			cin>>temp;
			sursum+=temp;
			if(sursum>resmax)
			{
				resmax=sursum;
				resright=i;
				resleft=curleft;
			}
			if(sursum<0)
			{
				sursum=0;
				curleft=i+1;
			}
		}
		printf("Case %d:\n%d %d %d\n",i, resmax, resleft, resright);
    printf(i==t?"":"\n");
	}
}
}

题意理解

题意是按照顺序进行不停的相加，假设每一次加一个数所得到的数据都另外储存在一个数组里面，则到最后进行每一步加法的大小比较，输出三组数据，第一个数据是不停相加过程中出现的最大值，第二个数据是相加过程中的起始点，注意，这里相加时若出现负数可以进行清零，然后起始点赋值成变成负值位置的下一个位置。假设中的数据实际不会用到只是为了方便解释题意，用数组进行储存每一步的相加数据太麻烦。第三个数据则是相加过程中的结束点。

对于最大值的判断：如何判断最大值是完成这个题目的首要问题，则需要一个累加的代码进行不断相加输入的数据，还需要一个判断程序，即if条件语句，进行判断是否大于“历届”最大值，最后需要一个空间储存最大值。首先定义一个空间resmax，进行初始化为零，接着对不停累加的变量sursum进行比较，与resmax进行比较，当前值大于结果值时更新resmax, resleft, resright,当前值小于0时更新curleft, cursum;。