斐波那契的变形

func numWays(n int) int {
	var cache map[int]int
	cache = make(map[int]int)
	cache[0] = 1
	cache[1] = 1
	for i := 2; i <= n; i++ {
		cache[i] = (cache[i-1] + cache[i-2]) % 1000000007
	}
	return cache[n]
}