Envío 577

Código

// Solution to https://codeo.app/problemas/0x25-suma-de-un-subarreglo
package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func solve(a, s []int, p, q int) {
	// O(1)
	sum := s[q] // a[0] + a[1] + ... + a[q]
	if p-1 >= 0 {
		sum -= s[p-1]
	}

	// Alternatively, this works too, and some people might like it more.
	// sum := s[q] - s[p] + a[p];
	fmt.Println(sum)
}

func main() {

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

	scanner.Scan()
	n, _ := strconv.Atoi(scanner.Text())

	a := make([]int, n)
	s := make([]int, n)
	sum := 0
	for i := 0; i < n; i++ {
		scanner.Scan()
		a[i], _ = strconv.Atoi(scanner.Text())
		sum += a[i]
		s[i] = sum
	}

	// s[i] = sum of a[0] + ... + a[i]
	var c int
	scanner.Scan()
	c, _ = strconv.Atoi(scanner.Text())

	for k := 0; k < c; k++ {
		var p, q int

		scanner.Scan()
		p, _ = strconv.Atoi(scanner.Text())
		scanner.Scan()

		q, _ = strconv.Atoi(scanner.Text())
		solve(a, s, p, q)
	}
}