剑指 10- II. 青蛙跳台阶问题

剑指 Offer 10- II. 青蛙跳台阶问题

//滚动数组，空间O1
func numWays(n int) int {
    prev , cur := 1, 1
    for i := 2; i <= n; i++ {
        temp := (cur + prev) %1000000007
        prev = cur
        cur = temp
    }
    return cur
}

//时空都是On
func numWays(n int) int {
    if n==1||n==0{
        return 1
    }
    if n==2{
        return 2
    }

    dp := make([]int, n+1)
    dp[0], dp[1] = 1, 1

    for i := 2; i <= n; i++ {
        dp[i] = (dp[i-1] + dp[i-2]) %1000000007
    } 
    return dp[n]
}