求最大子列和的几种方法

    给出一个数组a[]与数组长度N，求该数组中最大子列和。（子列由数组中连续的元素组成）

int MaxSubseqSum1(int a[], int N)   //O(n^3)
{
    int MaxSum = 0;
    for (int i = 0; i < N; i++)    //i为子列左边界
    {
        for (int j = i; j < N; j++)    //j为子列右边界
        {
            int TempSum = 0;
            for (int k = i; k <= j; k++)    //遍历子列内的元素
            {
                TempSum += a[k];
            }
            if ( TempSum > MaxSum )
            {
                MaxSum = TempSum;
            }
        }
    }
    return MaxSum;
}

int MaxSubseqSum2(int a[], int N)  //O(n^2)
{
    int MaxSum = 0;
    for (int i = 0; i < N; i++)
    {
        int TempSum = 0;
        for (int j = i; j < N; j++)
        {
            TempSum += a[j];
            if (TempSum > MaxSum)
            {
                MaxSum = TempSum;
            }
        }
    }
    return MaxSum;
}

int MaxSubseqSum3(int a[], int N)    //O(N)
{
    int MaxSum, TempSum;
    MaxSum = TempSum = 0;
    for (int i = 0; i < N; i++)
    {
        TempSum += a[i];
        if ( TempSum > MaxSum )
        {
            MaxSum = TempSum;
        }
        else if ( TempSum < 0 )    //关键：如果当前子列和为负，则不可能使后面的部分和增大，因此可舍弃
        {
            TempSum = 0;
        }
    }
    return MaxSum;
}