Input: Triangle = [ [1], [2,4], [6,4,9], [5,1,7,2] ]
Output: 8

Explanation: The given triangle

            1
           2 4
          6 4 9
         5 1 7 2

The minimum path sum from top to bottom:  1 + 2 + 4 + 1 = 8

             [1]
           [2]  4
           6 [4] 9
          5 [1] 7 2