Editorial for Stone Piles
Remember to use this editorial only when stuck, and not to copy-paste code from it. Please be respectful to the problem author and editorialist.
Submitting an official solution before solving the problem yourself is a bannable offence.
Submitting an official solution before solving the problem yourself is a bannable offence.
#include <bits/stdc++.h>
using namespace std;
#define MOD 1000000007
int solve(vector<int> a, int k)
{
int n = a.size();
int cnt = 0;
if(a.front() < k-1 || a.back() < k-1)
return 0;
for(int i = 0; i < n; ++i)
if(a[i] > k)
return 0;
for(int i = 0; i < n-1; ++i)
if(abs(a[i+1] - a[i]) > 1)
return 0;
int res = 1;
for(int i = 0; i < n-1; ++i)
if(a[i] == a[i+1] && a[i] != k)
res = (res*2) % MOD;
return res;
}
int main()
{
int n, k;
cin >> n >> k;
vector<int> a(n);
for(int i = 0; i < n; ++i)
cin >> a[i];
cout << solve(a, k) << endl;
return 0;
}