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typicalstairs Batch , stdin/stdout

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typicalstairs.html

typicalstairs

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 a1-th, a2-th, a3-th, \ldots, aM-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 ≤ N ≤ 105
  • 0 ≤ M ≤ N-1
  • 1 ≤ a1 < a2 < ... < aM ≤ N-1

Input

Input is given from Standard Input in the following format:

N M
a1
a2
 .
 .
 .
aM

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.

Tags

AtCoder, Dynamic Programming

Subtasks and Limits

Subtask Score #TC Time Memory Scoring
1100361s256MBMinimum
2031s256MBMinimum

Judge Compile Command

g++-8 ans.cpp -o typicalstairs -Wall -Wshadow -static -O2 -lm -m64 -s -w -std=gnu++17 -fmax-errors=512

Accepted Submissions

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Past Submissions

subIDUserTimeScore
mrJudge 09.05.20
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