Problem:
Score : 300 points

Problem Statement

There is a staircase with N steps. Takahashi is now standing at the foot of the stairs, that is, on the 0-th step.
He can climb up one or two steps at a time.

However, the treads of the a_1-th, a_2-th, a_3-th, \ldots, a_M-th steps are broken, so it is dangerous to set foot on those steps.

How many are there to climb up to the top step, that is, the N-th step, without setting foot on the broken steps?
Find the count modulo 1\ 000\ 000\ 007.

Constraints

1 \leq N \leq 10^5

0 \leq M \leq N-1

1 \leq a_1 < a_2 < ... < a_M \leq N-1

Input

Input is given from Standard Input in the following format:

N M
a_1
a_2
.
.
.
a_M

Output

Print the number of ways to climb up the stairs under the condition, modulo 1\ 000\ 000\ 007.

Sample Input 1

6 1
3

Sample Output 1

4

There are four ways to climb up the stairs, as follows:

0 \to 1 \to 2 \to 4 \to 5 \to 6

0 \to 1 \to 2 \to 4 \to 6

0 \to 2 \to 4 \to 5 \to 6

0 \to 2 \to 4 \to 6

Sample Input 2

10 2
4
5

Sample Output 2

0

There may be no way to climb up the stairs without setting foot on the broken steps.

Sample Input 3

100 5
1
23
45
67
89

Sample Output 3

608200469

Be sure to print the count modulo 1\ 000\ 000\ 007.

Solution in Go (1.6) (judge verdict: Runtime Error)

package main

import (
	"fmt"
	"math"
)

const d = 1000000007

func main() {
	var n, p int
	fmt.Scan(&n)
	fmt.Scan(&p)

	var n1 int64
	fmt.Scan(&n1)
	dans := make([]int64, p, p)
	dans[0] = n1
	mdans := map[int64]int64{
		n1: n1,
	}

	for index := 1; index < p; index++ {
		var n1 int64
		fmt.Scan(&n1)
		if dans[index-1] == n1 {
			continue
		}
		dans[index] = n1
		if math.Abs(float64(dans[index-1]-dans[index])) == 1 {
			fmt.Println(0)
			return
		}
		mdans[n1] = n1
	}

	dp := make([]int64, n+2, n+2)
	dp[0] = 1

	if _, ok := mdans[int64(1)]; !ok {
		dp[1] = 1
	}

	for index := 0; index < n; index++ {
		// fmt.Printf("%#v\n", Min(n, index+2))
		for j := index + 1; j <= Min(n, index+2); j++ {
			if _, ok := mdans[int64(j)]; !ok {
				dp[j] += dp[index]
				dp[j] %= d
			}
		}
	}

	// fmt.Printf("%#v\n", "******")
	// fmt.Printf("%#v\n", dp)
	fmt.Printf("%#v\n", dp[n])
}

func Min(nums ...int) int {
	if len(nums) == 0 {
		panic("function min() requires at least one argument.")
	}
	res := nums[0]
	for i := 0; i < len(nums); i++ {
		res = int(math.Min(float64(res), float64(nums[i])))
	}
	return res
}