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 PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php
list($n, $m)=explode(" ", fgets(STDIN));
$broken_stairs =[];
$zero_flag=0;
for($i=0; $i<$m; $i++){
	$broken_stairs[] = trim(fgets(STDIN));
	if($broken_stairs[$i]==0 && $broken_stairs[$i-1]==0){
		$zero_flag =1;
		break;
	}
}

function get_all_ways($n, $broken_stairs){
	$array = [];
	for($i=0; $i<=$n; $i++){
		if(!in_array($i, $broken_stairs)){
			if($i==0 || $i==1){
				$array[]=1;
			}elseif($array[$i-1]==0 && $array[$i-2]==0){
				return 0;
			}else{
				$array[] = $array[$i-1] + $array[$i-2];
			}
		}else{
			$array[] = 0;
		}
	}
	return $array[$n];
}

echo $zero_flag==1 ? 0 . "\n" : get_all_ways($n, $broken_stairs)%1000000007 . "\n";
?>