stock maximum profit
function StockPicker(arr) {
let lissf = arr[0]
let profit = -1
for(let i = 1; i < arr.length; i++) {
if(arr[i] > lissf) {
profit = Math.max(profit, arr[i] - lissf)
} else {
lissf = arr[i]
}
}
return profit
}