最大子序列和问题

//穷举法，复杂度O(n^3) 
long maxSubSum1(const vector<int>& a) 
{ 
       long maxSum = 0; 
       for (int i = 0; i < a.size(); i++) 
       { 
              for (int j = i; j < a.size(); j++) 
              { 
                     long thisSum = 0; 
 
                     for (int k = i; k <= j; k++) 
                     { 
                            thisSum += a[k]; 
                     } 
                     if (thisSum > maxSum) 
                            maxSum = thisSum; 
              } 
       } 
       return maxSum; 
}