#include <bits/stdc++.h> #define mod 1000000007 using namespace std; long long a[300000], dp[300000]; int main() { ios_base::sync_with_stdio(0); cin.tie(0); int n; cin >> n; for(int i = 0; i < n; ++i) cin >> a[i]; if(n <= 3000) { for(int i = 0; i < n; ++i) { long long sum = 0; for(int j = i; j >= 0; --j) { sum += a[j]; sum %= mod; if(sum%2 == 0) { if(j) dp[i] += dp[j-1]; else dp[i] += 1; dp[i] %= mod; } } } cout << dp[n-1]; return 0; } long long wyn = 1; int sum = 0; for(int i = 0; i < n-1; ++i) { sum += a[i]%2; if(sum%2 == 0) { wyn <<= 1; wyn %= mod; } } sum += a[n-1]; if(sum%2 == 0) cout << wyn; else cout << 0; 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 54 55 56 57 58 59 | #include <bits/stdc++.h> #define mod 1000000007 using namespace std; long long a[300000], dp[300000]; int main() { ios_base::sync_with_stdio(0); cin.tie(0); int n; cin >> n; for(int i = 0; i < n; ++i) cin >> a[i]; if(n <= 3000) { for(int i = 0; i < n; ++i) { long long sum = 0; for(int j = i; j >= 0; --j) { sum += a[j]; sum %= mod; if(sum%2 == 0) { if(j) dp[i] += dp[j-1]; else dp[i] += 1; dp[i] %= mod; } } } cout << dp[n-1]; return 0; } long long wyn = 1; int sum = 0; for(int i = 0; i < n-1; ++i) { sum += a[i]%2; if(sum%2 == 0) { wyn <<= 1; wyn %= mod; } } sum += a[n-1]; if(sum%2 == 0) cout << wyn; else cout << 0; return 0; } |