前缀和

问题引入

package mainimport ("fmt"
)func main() {var n, q, l, r intfmt.Scan(&n, &q)a := make([]int, n)ap := make([]int64, n + 1)ap[0] = 0for i := 0; i < n; i++ {fmt.Scan(&a[i])ap[i + 1] = ap[i] + int64(a[i])}for j := 0; j < q; j++ {fmt.Scan(&l, &r)fmt.Println(ap[r] - ap[l-1])}
}

考虑是不是输入太慢了，用Scanner试试

package mainimport ("bufio""fmt""os""strconv""strings"
)func main() {/*fmt.Scan()不会处理换行符，所以后面用sc.Scan()会读取换行符*//*改用fmt.Scanln()读取一行，且会丢弃换行符*/var n, q, l, r int//var s stringfmt.Scan(&n, &q)//fmt.Scanln(s)//values := strings.Split(s, " ")//n, _ = strconv.Atoi(values[0])//q, _ = strconv.Atoi(values[1])ap := make([]int64, n+1)ap[0] = 0sc := bufio.NewScanner(os.Stdin)sc.Scan()sc.Scan()strs := strings.Split(sc.Text(), " ")for i := range strs {val, _ := strconv.Atoi(strs[i])ap[i+1] = ap[i] + int64(val)}for i := 0; i < q; i++ {fmt.Scan(&l, &r)fmt.Println(ap[r] - ap[l-1])}
}// package main// import (
//     "fmt"
// )// func main() {
//     var n, q, l, r int
//     fmt.Scan(&n, &q)
//     a := make([]int, n)
//     ap := make([]int64, n + 1)
//     ap[0] = 0//     for i := 0; i < n; i++ {
//         fmt.Scan(&a[i])
//         ap[i + 1] = ap[i] + int64(a[i])
//     }
//     for j := 0; j < q; j++ {
//         fmt.Scan(&l, &r)
//         fmt.Println(ap[r] - ap[l-1])
//     }
// }

本地goland运行：

但牛客上运行：

于是，开始对输入输出好好研究：

package mainimport ("bufio""fmt""os"
)func main() {var (n, q, l, r intin = bufio.NewReader(os.Stdin)out = bufio.NewWriter(os.Stdout))fmt.Fscan(in, &n, &q)a := make([]int, n)ap := make([]int64, n+1)ap[0] = 0for i := 0; i < n; i++ {fmt.Fscan(in, &a[i])ap[i+1] = ap[i] + int64(a[i])}for j := 0; j < q; j++ {fmt.Fscan(in, &l, &r)fmt.Fprintln(out, ap[r] - ap[l - 1])// fmt.Println(ap[r] - ap[l-1])out.Flush()}
}

那么在此前提下，如果第二行输入不一个个读入，用整行读入呢？
（其实到这，我就有了对自己之前行为的评价：之前代码的各种输入输出用的很混乱，想用哪一套就彻底用哪一套呗，快不快慢不慢的，看着就恶心）

package main// 前缀和很简单，往往输入数据会很变态，所以不能用fmt.Scan()和fmt.Println()
// 有好几种优化的输入输出// 用封装好的bufio.NewReader(os.Stdin)和bufio.NewWriter(os.Stdout)/*
var (n, q, l, r intin         = bufio.NewReader(os.Stdin)out        = bufio.NewWriter(os.Stdout)
)func main() {fmt.Fscan(in, &n, &q)a := make([]int, n)ap := make([]int64, n+1)ap[0] = 0for i := 0; i < n; i++ {fmt.Fscan(in, &a[i])ap[i+1] = ap[i] + int64(a[i])}for j := 0; j < q; j++ {fmt.Fscan(in, &l, &r)fmt.Fprintln(out, ap[r]-ap[l-1])out.Flush()}
}
*/// 用适合于整行读取的组合方法
/*
sc := bufio.NewScanner(os.Stdin)
bs := make([]byte, 20000 * 1024) //设置缓冲区的最大读取
readLine = func() (res string) {sc.Scan() //读一行l := strings.Split(sc.Text(), " ")var res stringfor _, s := range l {res += s}return
}
out = bufio.NewWriter(os.Stdout)scanner.Buffer(bs, len(bs)) //设置缓冲区的最大读取
cur := readLine()
fmt.Fprint(out, cur)
out.Flush()
*/import ("bufio""fmt""os""strconv""strings"
)var (n, p, l, r intsc         = bufio.NewScanner(os.Stdin) //按行扫描器out        = bufio.NewWriter(os.Stdout) //文件输出流（要用fmt.Fprint(out, ...)）bs         = make([]byte, 20000*1024)   //设置缓冲区最大读取readLine   = func() (res []int) {       //把读取一行的操作封装成一个匿名函数sc.Scan()                             //扫描器读取一行strs := strings.Split(sc.Text(), " ") //将读取的字符串分割成切片res = make([]int, len(strs))          //这一句不能遗漏，返回值是切片类型，必须要有初始化for i, s := range strs {              //将切片中的每个元素转换为int类型，再存入返回值切片里x, _ := strconv.Atoi(s)res[i] = x}return}
)func main() {sc.Buffer(bs, len(bs))         //设置缓冲区读取最大数量cur1 := readLine()             //读第一行ap := make([]int64, cur1[0]+1) //前缀和数组（切片）cur2 := readLine()             //读第二行for i := range cur2 {ap[i+1] = ap[i] + int64(cur2[i]) //求前缀和}for i := 0; i < cur1[1]-1; i++ { //求要求的区间内的数值和cur := readLine()fmt.Fprintln(out, ap[cur[1]]-ap[cur[0]-1])}//最后一组单独写是为了防止最后多个换行cur := readLine()fmt.Fprint(out, ap[cur[1]]-ap[cur[0]-1])//最后一下给Flush出来out.Flush()
}