Faster input scanning

Question

I am attempting to solve the SPOJ question that can be found here

Following is my solution:

package main

import \"fmt\"
import \"bufio\"
import \"os         


        

Answer 1

I coded 3 versions to compare them. The first using fmt.Scanf("%d", &v), the second converting numbers from bytes (like @icza), and the third converting using strconv.Atoi. To use the functions I initializated scanner in that way:

scanner := bufio.NewScanner(os.Stdin)
scanner.Split(bufio.ScanWords)

So, every time I call scanner.Scan, it returns a token splitted by spaces. And the functions follow:

func scanFromBytes(scanner *bufio.Scanner) (n int) {
    scanner.Scan()

    buf := scanner.Bytes()
    for _, v := range buf {
        n = n*10 + int(v-'0')
    }

    return
}

And:

func scanAtoi(scanner *bufio.Scanner) (n int) {
    scanner.Scan()
    
    n, _ = strconv.Atoi(scanner.Text())

    return
}

I have tested with a big file (40k tests), reading about 8 integers per test. The fmt.Scanf solution, takes about 1.9s, as expected (more than the others). In the two functions I got about 0.8s. But the scanAtoi always takes about 0.05s less than scanFromBytes, except for the very first time (maybe some caching occurs).