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 Java8 (OpenJDK 1.8.0) (judge verdict: Runtime Error)

import java.lang.reflect.Array;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int[] first = new int[] {Integer.parseInt(sc.next()),Integer.parseInt(sc.next())}; 
		int[] second = new int[first[1]];
		for(int i=0; i<first[1]; i++) {
			second[i] = Integer.parseInt(sc.next());
		}
//		int[] first = new int[] {100,5};
//		int[] second = new int[] {1,23,45,67,89};

		
		boolean check = true;
		for(int i=0; i<first[1]-1; i++) {
			try {
				if(second[i] == second[i+1]-1) {
					check = false;
					break;
				}
			}catch (Exception e) {
				check = false;
				break;
			}
		}
		if(check == false) {
			System.out.println(0);
			return;
		}
		
		int firstStep = 0;
		int lastStep = second[0]-1;
		BigInteger[] bArray = new BigInteger[second.length+1];
		BigInteger fibonacchi = new BigInteger("1");
		BigInteger a = new BigInteger("0");
		BigInteger b = new BigInteger("1");
		
		for(int i=0; i<=second.length; i++) {
			a = new BigInteger("0");
			b = new BigInteger("1");
			for(int j=firstStep+1; j<=lastStep; j++) {
//				System.out.println("tets"+j);
//				System.out.println("tet"+lastStep);
				fibonacchi = fibonacchi(a, b);
				a = b;
				b = fibonacchi;
			}
			bArray[i] = fibonacchi;
			try {
				firstStep = second[i]+1;
				lastStep = second[i+1]-1;
			}catch (Exception e) {
				firstStep = second[second.length-1]+1;
				lastStep = first[0];
			}
		}
		BigInteger result = new BigInteger("1");
		for(BigInteger bi:bArray) {
			result = result.multiply(bi);
		}
//		long result = 1;
//		for(int i=0; i<list.size(); i++) {
////			System.out.println(result);
//			result *= list.get(i).get(list.get(i).size()-1);
//		}
//		System.out.println(result);
		System.out.println(result.mod(new BigInteger("1000000007")));
	}
	public static BigInteger fibonacchi(BigInteger b1,BigInteger b2) {
//		System.out.println(b1.add(b2));
		return b1.add(b2);
	}
}