The stock picker takes in an array of values (integers) and returns an array with the indices of the values that have the greatest "profit"
Examples:
stock_picker([3, 2, 2, 1, 2, 5, 3, 4, 2]) => [3, 5], profit: $5 - $1 = $4
stock_picker([6, 2, 4, 1]) => [1, 2], profit: $4 - $2 = $2
stock_picker([4, 2, 1]) => [], do not buy.