hdu1003 Max Sum (求连续的和最大的自链

Max Sum

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 242181    Accepted Submission(s): 57180

Problem Description

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

题意：t组数据，长度为n的字符串，找出一段连续且和最大的字符串
#include<stdio.h>
#include<iostream>
#include<algorithm>
using namespace std;
const int inf=0x3f3f3f3f;
int main()
{
    int t;
    scanf("%d",&t);
    int k=t;
    while(t--)
    {
        int n;
        scanf("%d",&n);
        int maxx=-inf,sum=0;
        int x=1,y=0,temp=1;//temp用来标记起点
        for(int i=0; i<n; i++)
        {
            int a;
            scanf("%d",&a);
            sum+=a;
            if(sum>maxx)//两个if判断不能换位置，例5 -1 -2 -3 -4 -5
                //这样会提前改变sum和temp的值，从而错误
            {
                maxx=sum;
                x=temp;
                y=i+1;
            }
            if(sum<0)
            {
                sum=0;
                temp=i+2;//如果不用temp标记起点，直接用x的话例：5 -1 -2 -3 -4 -5
                //x会一直加下去，输出就会出错
                //x=i+1;
            }

        }
        printf("Case %d:
%d %d %d
",k-t,maxx,x,y);
        if(t!=0)
            printf("
");
    }
    return 0;
}
这个是错误的代码，我考虑一下我错哪了
#include<stdio.h>
#include<iostream>
#include<algorithm>
using namespace std;
const int inf=0x3f3f3f3f;
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        int n;
        scanf("%d",&n);
        int maxx=-inf,sum=0;
        int x=0,y=0,temp=1;
        //这种代码，有特别多的弊端，
        //值全为0时，maxx，x，y都不对
        //还有只要sum>0都能进入那个循环，y就会一直加,也是错的
        for(int i=0;i<n;i++)
        {
            int a;
            scanf("%d",&a);
            sum+=a;
            if(sum<0)
            {
                x=i+1;
                y=i+1;
                sum=0;
            }
            else
            {
                maxx=max(maxx,sum);
                y+=1;
            }
        }
    }
}