241. Different Ways to Add Paren

Given a string of numbers and operators, return all possible results from computing all the different possible ways to group numbers and operators. The valid operators are+,-and*.

Example 1   Input:"2-1-1".  ((2-1)-1) = 0  (2-(1-1)) = 2  Output:[0, 2]
Example 2   Input:"2*3-4*5"  (2*(3-(4*5))) = -34 ((2*3)-(4*5)) = -14   ((2*(3-4))*5) = -10  (2*((3-4)*5)) = -10
(((2*3)-4)*5) = 10  Output:[-34, -14, -10, -10, 10]

符号左边部分与右边部分分别计算，  divide and conquer.