Difference between bufio scanner and reader

if i am using these reader then it’s accepted the answer but if i trided the same with scanner it’s not accepting the answer

can anyone please explain me this behavior ?

    `func main() {
// your code goes here
reader := bufio.NewReader(os.Stdin)
T, _ := reader.ReadString('\n')
t, _ := strconv.Atoi(strings.TrimSpace(T))
for ; t > 0; t-- {
	reader.ReadString('\n')
	Arr, _ := reader.ReadString('\n')
	arr := strings.Split(strings.TrimSpace(Arr), " ")
	ans := findNextGreaterNumber(arr)
	fmt.Println(ans)
}

}`

func main() {

f, err := os.Open("input.txt")

if err != nil {
	panic(err)
}
scanner := bufio.NewScanner(f)
scanner.Scan()
T := scanner.Text()
t, _ := strconv.Atoi(T)
for ; t > 0; t-- {
	scanner.Scan()
	scanner.Scan()
	Arr := scanner.Text()
	arr := strings.Split(Arr, " ")
	ans := findNextGreaterNumber(arr)
	fmt.Println(ans)
}

}