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https://git.sb/baoshuo/OI-codes.git
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95 lines
1.8 KiB
C++
95 lines
1.8 KiB
C++
#include <iostream>
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#include <bitset>
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#include <cmath>
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#include <cstring>
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#include <queue>
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#include <vector>
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using std::cin;
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using std::cout;
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const char endl = '\n';
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const int N = 30001;
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int n, m, l, s, t;
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std::vector<std::pair<int, short>> g[N * 101];
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int dist[N * 101];
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std::bitset<N * 101> vis;
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int spfa() {
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memset(dist, 0x3f, sizeof(dist));
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std::queue<int> q;
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dist[s] = 0;
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q.push(s);
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vis[s] = true;
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while (!q.empty()) {
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int u = q.front();
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q.pop();
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vis[u] = false;
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for (auto t : g[u]) {
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int v = t.first;
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short w = t.second;
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if (dist[v] > dist[u] + w) {
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dist[v] = dist[u] + w;
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if (!vis[v]) {
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q.push(v);
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vis[v] = true;
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}
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}
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}
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}
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return dist[t] == 0x3f3f3f3f ? -1 : dist[t];
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}
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int main() {
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std::ios::sync_with_stdio(false);
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cin.tie(nullptr);
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cin >> n >> m;
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l = std::min(static_cast<int>(std::sqrt(n)), 100);
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for (int i = 1, b, p; i <= m; i++) {
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cin >> b >> p;
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b++;
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if (i == 1) s = b;
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if (i == 2) t = b;
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if (p <= l) {
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g[b].emplace_back(p * n + b, 0);
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} else {
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for (int j = 1; b + j * p <= n; j++) {
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g[b].emplace_back(b + j * p, j);
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}
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for (int j = 1; b - j * p > 0; j++) {
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g[b].emplace_back(b - j * p, j);
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}
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}
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}
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for (int i = 1; i <= l; i++) {
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for (int j = 1; j <= n; j++) {
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g[i * n + j].emplace_back(j, 0);
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}
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for (int j = 1; j <= n - i; j++) {
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g[i * n + j].emplace_back(i * n + j + i, 1);
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g[i * n + j + i].emplace_back(i * n + j, 1);
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}
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}
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cout << spfa() << endl;
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return 0;
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}
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