Write a function named alternatingSum that takes a vector of integers, and returns the alternating sum of all elements in the vector. For example, if alternatingSum is called with a vector numbers containing then it computes 1 3 2 5 3 1 5 11 20 1-3+2 5+3-1+5-11+ 20 = 11 Define your function alternatingSum using the prototype int alternatingSum (const vector & numbers);