Pivot Index--Google

 1 public int PivotIndex(int[] nums)
 2         {
 3             if (nums == null || nums.Length == 0)
 4             {
 5                 return -1;
 6             }
 7             int l = nums.Length;
 8             int sum = 0; int leftsum = 0;
 9             for (int i = 0; i < l; i++)
10             {
11                 sum +=nums[i];
12             }
13             for (int j=0; j< l; j++)
14             {
15                 if (sum - nums[j] - leftsum == leftsum)
16                 {
17                     return j;
18                 }
19                 else
20                     leftsum += nums[j];
21             }
22             return -1;
23         }