I have written a mergeSort function, which sorted 1 million integers in 750ms, but it takes 9 seconds to take input.
This is how I have taken input to my slice, which is to be sorted.
code snippet:
array := make([]int,n)
for i := 0; i < n; i++ {
fmt.Scanf("%d",&array[i])
}
What I need is, an efficient way to take integers as input into a slice. Input contains only integers, seperated by space or each integer in new-line.
Sample Input 1:
3
9
1
13
Sample Input 2:
3 9 1 13
If efficient solution is available for any one type of Input, it would suffice
package main
import (
"io/ioutil"
"os"
)
// inp is a variable in which we store our whole input
var inp []byte
// loc is used as index and remember till where we have seen our input
var loc int
func main() {
// we read whole input and store it in inp and then append '
', so
// that we don't get any type index out of bound error, while
// scanning the last digit.
inp, _ = ioutil.ReadAll(os.Stdin)
inp = append(inp, '
')
// when ever scanInt is called, it will return single value of type int
// usage:
// n := scanInt()
}
func scanInt() (res int) {
// skip if byte value doesn't belong to integer and break when it is
// an integer
for ; inp[loc] < 48 || inp[loc] > 57; loc++ {
}
// If it is an integer parse it completely else break return the result
for ; inp[loc] > 47 && inp[loc] < 58 ; loc++ {
res = (res << 1 ) + (res << 3) + int(inp[loc]-48)
}
return
}
On the assumption that your input is space separated signed integers (in base 10), try the following:
s := bufio.NewScanner(os.StdIn)
s.Split(bufio.ScanWords)
i := 0
for s.Scan() && i < n {
dest[i], _ = strconv.ParseInt(s.Text(), 10, 64)
i++
}
This shows with a quick benchmark to be about 5 times faster than using fmt.Scanf. It could probably be further optimised by writing a custom split function that did not worry about parsing UTF-8 runes and simply split on ' '.