#include <algorithm> #include <cstdio> const int mod = 1000000007; const int max_n = 400000; int n; int a[max_n]; int mmap[max_n]; int dp[max_n]; std::pair<int, int> b[max_n]; const int czapa = 524288; int odd[2 * czapa + 1]; int even[2 * czapa + 1]; void add(int tree[], int index, int val) { index += czapa; tree[index] += val; if (tree[index] >= mod) tree[index] -= mod; while (index > 1) { index /= 2; tree[index] += val; if (tree[index] >= mod) tree[index] -= mod; } } int count_le(int tree[], int index) { ++index; index += czapa; int ret = 0; while (index > 1) { if (index % 2 == 1) { ret += tree[index - 1]; if (ret >= mod) ret -= mod; } index /= 2; } return ret; } int count_a(int tree[], int index) { index += czapa; int ret = 0; while (index > 1) { if (index % 2 == 0) { ret += tree[index + 1]; if (ret >= mod) ret -= mod; } index /= 2; } return ret; } int main() { for (int i = 0; i < 2 * czapa + 1; ++i) odd[i] = even[i] = 0; scanf("%d", &n); a[0] = 0; b[0].first = 0; b[0].second = 0; for (int i = 1; i <= n; ++i) { scanf("%d", a + i); a[i] = a[i] + a[i - 1]; if (a[i] >= mod) a[i] -= mod; b[i].first = a[i]; b[i].second = i; } std::sort(b, b + n + 1); int cnt = 0; for (int i = 0; i < n + 1; ++i) { if (i != 0 && b[i] != b[i - 1]) { ++cnt; } mmap[b[i].second] = cnt; } add(even, mmap[0], 1); dp[0] = 1; for (int i = 1; i <= n; ++i) { dp[i] = 0; if (a[i] % 2 == 0) { dp[i] = (count_le(even, mmap[i]) + count_a(odd, mmap[i])) % mod; add(even, mmap[i], dp[i]); } else { dp[i] = (count_le(odd, mmap[i]) + count_a(even, mmap[i])) % mod; add(odd, mmap[i], dp[i]); } } printf("%d\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 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 | #include <algorithm> #include <cstdio> const int mod = 1000000007; const int max_n = 400000; int n; int a[max_n]; int mmap[max_n]; int dp[max_n]; std::pair<int, int> b[max_n]; const int czapa = 524288; int odd[2 * czapa + 1]; int even[2 * czapa + 1]; void add(int tree[], int index, int val) { index += czapa; tree[index] += val; if (tree[index] >= mod) tree[index] -= mod; while (index > 1) { index /= 2; tree[index] += val; if (tree[index] >= mod) tree[index] -= mod; } } int count_le(int tree[], int index) { ++index; index += czapa; int ret = 0; while (index > 1) { if (index % 2 == 1) { ret += tree[index - 1]; if (ret >= mod) ret -= mod; } index /= 2; } return ret; } int count_a(int tree[], int index) { index += czapa; int ret = 0; while (index > 1) { if (index % 2 == 0) { ret += tree[index + 1]; if (ret >= mod) ret -= mod; } index /= 2; } return ret; } int main() { for (int i = 0; i < 2 * czapa + 1; ++i) odd[i] = even[i] = 0; scanf("%d", &n); a[0] = 0; b[0].first = 0; b[0].second = 0; for (int i = 1; i <= n; ++i) { scanf("%d", a + i); a[i] = a[i] + a[i - 1]; if (a[i] >= mod) a[i] -= mod; b[i].first = a[i]; b[i].second = i; } std::sort(b, b + n + 1); int cnt = 0; for (int i = 0; i < n + 1; ++i) { if (i != 0 && b[i] != b[i - 1]) { ++cnt; } mmap[b[i].second] = cnt; } add(even, mmap[0], 1); dp[0] = 1; for (int i = 1; i <= n; ++i) { dp[i] = 0; if (a[i] % 2 == 0) { dp[i] = (count_le(even, mmap[i]) + count_a(odd, mmap[i])) % mod; add(even, mmap[i], dp[i]); } else { dp[i] = (count_le(odd, mmap[i]) + count_a(even, mmap[i])) % mod; add(odd, mmap[i], dp[i]); } } printf("%d\n", dp[n]); return 0; } |