主体思路

快速幂+费马小定理

注意细节

在go中， 可以不用特意用int64

基础代码

package main
import (
    "fmt"
    "bufio"
    "os"
    )

const (
    N = 100010
    mod = 1e9 + 7
    )    

var (
    out = bufio.NewWriter(os.Stdout)
    in = bufio.NewReader(os.Stdin)

    n int
    fact, infact [N]int
    )

func qmi(a, k, p int) int {
    res := 1
    for k > 0 {
        if k & 1 > 0 { res = res * a % p }
        a = a * a % p
        k >>= 1
    }
    return res 
}

func main() {
    fact[0], infact[0] = 1, 1 
    for i := 1; i < N; i++ {
        fact[i] = fact[i - 1] * i % mod
        infact[i] = infact[i - 1] * qmi(i, mod - 2, mod) % mod
    }

    fmt.Fscan(in, &n)
    for; n > 0; n-- {
        a, b := 0, 0 
        fmt.Fscan(in, &a, &b)
        fmt.Fprint(out, fact[a] * infact[b] % mod * infact[a - b] % mod, "\n")
    }
    out.Flush()
}