#include <bits/stdc++.h> using namespace std; const int MOD = 1000 * 1000 * 1000 + 7; int add(int x, int y) { x += y; if (x >= MOD) { x -= MOD; } return x; } struct PointUpdateTree { typedef int val_t; val_t getValInit(int i) { return 0; } val_t combine(const val_t &a, const val_t &b) { return add(a, b); } int p = 1; vector <val_t> tree; PointUpdateTree(int n) { while (p < n) p *= 2; int m = 2 * p - 1; tree.resize(m); for (int i = p - 1; i < m; i++) { tree[i] = getValInit(i - p + 1); } for (int i = p - 2; i >= 0; i--) { tree[i] = combine(tree[2 * i + 1], tree[2 * i + 2]); } } int par(int x) { return (x - 1) / 2; } void update(int l, val_t v) { l += p - 1; tree[l] = v; while (l > 0) { l = par(l); tree[l] = combine(tree[2 * l + 1], tree[2 * l + 2]); } } val_t query(int l, int r) { if (l > r) { return 0; } l += p - 1; r += p - 1; if (l == r) { return tree[l]; } val_t ans = combine(tree[l], tree[r]); while (par(l) != par(r)) { if (l % 2 == 1) ans = combine(ans, tree[l + 1]); if (r % 2 == 0) ans = combine(ans, tree[r - 1]); l = par(l); r = par(r); } return ans; } }; int solve(int n, vector <int> &arr) { vector <int> pref(n + 1, 0); for (int i = 1; i <= n; i++) { pref[i] = add(pref[i - 1], arr[i - 1]); } vector <pair<int,int>> remAndPos(n + 1); for (int i = 0; i <= n; i++) { remAndPos[i] = {pref[i], i}; } auto remAndPosSorted = remAndPos; sort(remAndPosSorted.begin(), remAndPosSorted.end()); vector <vector<pair<int,int>>> remForParity(2); for (auto &e : remAndPosSorted) { remForParity[e.first % 2].push_back(e); } vector <PointUpdateTree> dpForParity; for (int par = 0; par <= 1; par++) { dpForParity.emplace_back(remForParity[par].size()); } vector <int> dp(n + 1, 0); dp[0] = 1; auto recordDP = [&](int i) { int par = pref[i] % 2; int idx = lower_bound( remForParity[par].begin(), remForParity[par].end(), remAndPos[i] ) - remForParity[par].begin(); dpForParity[par].update(idx, dp[i]); }; recordDP(0); for (int i = 1; i <= n; i++) { int par = pref[i] % 2; int parNeg = 1 - par; pair <int,int> e = {pref[i], n + 1}; int jHigh = upper_bound( remForParity[par].begin(), remForParity[par].end(), e ) - remForParity[par].begin() - 1; dp[i] = add(dp[i], dpForParity[par].query(0, jHigh)); int jLow = upper_bound( remForParity[parNeg].begin(), remForParity[parNeg].end(), e ) - remForParity[parNeg].begin(); dp[i] = add(dp[i], dpForParity[parNeg].query(jLow, (int) remForParity[parNeg].size() - 1)); recordDP(i); } return dp[n]; } int main() { ios_base::sync_with_stdio(false); int n; cin >> n; vector <int> arr(n); for (int &ai : arr) { cin >> ai; } cout << solve(n, arr); 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 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 | #include <bits/stdc++.h> using namespace std; const int MOD = 1000 * 1000 * 1000 + 7; int add(int x, int y) { x += y; if (x >= MOD) { x -= MOD; } return x; } struct PointUpdateTree { typedef int val_t; val_t getValInit(int i) { return 0; } val_t combine(const val_t &a, const val_t &b) { return add(a, b); } int p = 1; vector <val_t> tree; PointUpdateTree(int n) { while (p < n) p *= 2; int m = 2 * p - 1; tree.resize(m); for (int i = p - 1; i < m; i++) { tree[i] = getValInit(i - p + 1); } for (int i = p - 2; i >= 0; i--) { tree[i] = combine(tree[2 * i + 1], tree[2 * i + 2]); } } int par(int x) { return (x - 1) / 2; } void update(int l, val_t v) { l += p - 1; tree[l] = v; while (l > 0) { l = par(l); tree[l] = combine(tree[2 * l + 1], tree[2 * l + 2]); } } val_t query(int l, int r) { if (l > r) { return 0; } l += p - 1; r += p - 1; if (l == r) { return tree[l]; } val_t ans = combine(tree[l], tree[r]); while (par(l) != par(r)) { if (l % 2 == 1) ans = combine(ans, tree[l + 1]); if (r % 2 == 0) ans = combine(ans, tree[r - 1]); l = par(l); r = par(r); } return ans; } }; int solve(int n, vector <int> &arr) { vector <int> pref(n + 1, 0); for (int i = 1; i <= n; i++) { pref[i] = add(pref[i - 1], arr[i - 1]); } vector <pair<int,int>> remAndPos(n + 1); for (int i = 0; i <= n; i++) { remAndPos[i] = {pref[i], i}; } auto remAndPosSorted = remAndPos; sort(remAndPosSorted.begin(), remAndPosSorted.end()); vector <vector<pair<int,int>>> remForParity(2); for (auto &e : remAndPosSorted) { remForParity[e.first % 2].push_back(e); } vector <PointUpdateTree> dpForParity; for (int par = 0; par <= 1; par++) { dpForParity.emplace_back(remForParity[par].size()); } vector <int> dp(n + 1, 0); dp[0] = 1; auto recordDP = [&](int i) { int par = pref[i] % 2; int idx = lower_bound( remForParity[par].begin(), remForParity[par].end(), remAndPos[i] ) - remForParity[par].begin(); dpForParity[par].update(idx, dp[i]); }; recordDP(0); for (int i = 1; i <= n; i++) { int par = pref[i] % 2; int parNeg = 1 - par; pair <int,int> e = {pref[i], n + 1}; int jHigh = upper_bound( remForParity[par].begin(), remForParity[par].end(), e ) - remForParity[par].begin() - 1; dp[i] = add(dp[i], dpForParity[par].query(0, jHigh)); int jLow = upper_bound( remForParity[parNeg].begin(), remForParity[parNeg].end(), e ) - remForParity[parNeg].begin(); dp[i] = add(dp[i], dpForParity[parNeg].query(jLow, (int) remForParity[parNeg].size() - 1)); recordDP(i); } return dp[n]; } int main() { ios_base::sync_with_stdio(false); int n; cin >> n; vector <int> arr(n); for (int &ai : arr) { cin >> ai; } cout << solve(n, arr); return 0; } |