题目：给出一个指定整形数组，求从数组某下标开始连续求和的”最大值“，并给出”起始“及”结束“的下标
如：给定数组[-1，8，-6，7，-10，-3，3，2] 那么连续求和最大值是7，开始下标是1、结束是3，即是[8,-6,7]的和。

思路：

从数组起始位置向后遍历，抛弃和为负数的子数组，加上和为正数的子数组。（想象一个滑动窗口不停向右移动）

代码:

type Response struct {
    Start  int
    End    int
    MaxSum int
}

func CaculateMaxSum(numlist []int) Response {
    switch len(numlist) {
    case 0:
        return Response{-1, -1, 0}
    case 1:
        return Response{0, 0, numlist[0]}
    default:

    }
    sum := numlist[0]
    sumToCurrent := numlist[0]
    start, end := 0, 0
    for index, num := range numlist {
        //abando negative sum
        if sum < 0 && num > sum {
            start, end, sum = index, index, num
            sumToCurrent = num
        } else if sum > 0 && (sumToCurrent-sum)+num > 0 {
            //sum the  current  value
            start, end, sum = start, index, sumToCurrent+num
            sumToCurrent = sum
        } else {
            //update sumToCurrent
            sumToCurrent = sumToCurrent + num
        }

    }

    return Response{start, end, sum}
}


func TestCaculateMaxSum(t *testing.T){
    testlist := [][]int{
        []int{-1, 8, -7, 6, -10, -3, 3, 2},
        []int{-8, -7, -6, -10, -3, -5},
        []int{-8, -7, 6, -1, -3, 5},
    }

    for _, numlist := range testlist {
        rsp := CaculateMaxSum(numlist)
        t.Logf("start:%v, end:%v, sum:%v\n", rsp.Start, rsp.End, rsp.MaxSum)
    }
}