最大子序列和求解 最優算法O(N)

/**
* Linear-time maximum contiguous subsequence sum algorithm.
*/
int maxSubSum4(const vector<int> & a)
{
    int maxSum=0,thisSum=0;
    for( int j=0;i<a.size();j++)
    {
       thisSum+=a[j];
       if(thisSum>maxSum)
           maxSum=thisSum;
       else if( thisSum < 0 )
            thisSum=0;
    }
    retrun maxSum;
}