题解 | 牛牛学数列4

package main

import (
	"fmt"
)

func main() {
	var n int
	fmt.Scan(&n)
	res := 0
	for i := 1; i <= n; i++ {
		res += sum(i)
	}
	fmt.Print(res)
}

func sum(n int) int {
	if n == 1 {
		return 1
	}
	res := make([]int, 2)
	res[0] = 1
	for i := 2; i <= n; i++ {
		res[1] = res[0] + i
		res[0] = res[1]
	}
	return res[1]
}