#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(...) begin(__VA_ARGS__) , end(__VA_ARGS__)
#define boost {ios_base::sync_with_stdio(false); cin.tie(); cout.tie();}
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef vector <int> vi;
typedef pair<int,int> PII;
typedef pair<ll,ll> PLL;
constexpr ll nax = 3e5+6969, INF = 2e9+6969, mod = 1e9 + 7;
int n;
ll t[nax], pref[nax], dp[nax], odd, even;
int main()
{
scanf("%d", &n);
for(int i=1;i<=n;i++)
{
scanf("%lld", &t[i]);
pref[i] = pref[i-1] + t[i];
if(pref[i] >= mod) pref[i] -= mod;
}
for(int i=1;i<=n;i++) pref[i] %= 2;
even = 1;
dp[0] = 1;
for(int i=1;i<=n;i++)
{
if(pref[i]%2 == 1)
{
dp[i] = odd;
odd += dp[i];
odd %= mod;
}
else
{
dp[i] = even;
even += dp[i];
even %= mod;
}
}
printf("%lld\n", dp[n]);
return 0;
}
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 | #define pb push_back #define mp make_pair #define fi first #define se second #define all(...) begin(__VA_ARGS__) , end(__VA_ARGS__) #define boost {ios_base::sync_with_stdio(false); cin.tie(); cout.tie();} #include <bits/stdc++.h> using namespace std; typedef long long ll; typedef unsigned long long ull; typedef long double ld; typedef vector <int> vi; typedef pair<int,int> PII; typedef pair<ll,ll> PLL; constexpr ll nax = 3e5+6969, INF = 2e9+6969, mod = 1e9 + 7; int n; ll t[nax], pref[nax], dp[nax], odd, even; int main() { scanf("%d", &n); for(int i=1;i<=n;i++) { scanf("%lld", &t[i]); pref[i] = pref[i-1] + t[i]; if(pref[i] >= mod) pref[i] -= mod; } for(int i=1;i<=n;i++) pref[i] %= 2; even = 1; dp[0] = 1; for(int i=1;i<=n;i++) { if(pref[i]%2 == 1) { dp[i] = odd; odd += dp[i]; odd %= mod; } else { dp[i] = even; even += dp[i]; even %= mod; } } printf("%lld\n", dp[n]); return 0; } |
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