This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define dl double
#define st first
#define nd second
#define II pair <int, int>
using namespace std;
const int N = 5 + 1e5;
const int inf = 7 + 1e9;
int n, m;
vector <int> b, p;
namespace subtask123 {
void main() {
vector <vector <int>> g(n);
for (int i = 1; i <= m; i ++)
g[b[i]].push_back(i);
vector <vector <II>> adj(m + 1);
for (int i = 1; i <= m; i ++) {
if (p[i] == 0)
continue;
int x = b[i], w = 0;
while (x >= 0) {
for (int j : g[x])
adj[i].push_back({j, w});
x -= p[i];
w ++;
}
x = b[i]; w = 0;
while (x + p[i] < n) {
x += p[i];
w ++;
for (int j : g[x])
adj[i].push_back({j, w});
}
}
vector <int> f(m + 1, inf);
priority_queue <II> q;
q.push({-(f[1] = 0), 1});
while (!q.empty()) {
int du = -q.top().st, u = q.top().nd;
q.pop();
if (f[u] < du)
continue;
for (auto z : adj[u]) {
int v = z.st, w = z.nd;
if (du + w < f[v])
q.push({-(f[v] = du + w), v});
}
}
if (f[2] == inf)
f[2] = -1;
cout << f[2];
}
}
namespace subtask4 {
void main() {
vector <vector <int>> g(n);
map <II, int> f;
for (int i = 1; i <= m; i ++)
g[b[i]].push_back(p[i]);
deque <II> q;
q.push_back({b[1], p[1]});
f[{b[1], p[1]}] = 0;
while (!q.empty()) {
int u = q.front().st, w = q.front().nd;
q.pop_front();
int du = f[{u, w}];
for (int w_ : g[u])
if (f.find({u, w_}) == f.end()) {
q.push_front({u, w_});
f[{u, w_}] = du;
}
for (int i = -1; i <= 1; i ++)
if (i != 0) {
int v = u + w * i;
if (v >= 0 && v < n && f.find({v, w}) == f.end()) {
q.push_back({v, w});
f[{v, w}] = du + 1;
}
}
}
int ans = inf;
for (int i = 1; i <= 30000; i ++)
if (f.find({b[2], i}) != f.end())
ans = min(ans, f[{b[2], i}]);
if (ans == inf)
ans = -1;
cout << ans;
}
}
int main() {
#define TASKNAME ""
ios_base :: sync_with_stdio (0);
cin.tie (0);
if ( fopen( TASKNAME".inp", "r" ) ) {
freopen (TASKNAME".inp", "r", stdin);
freopen (TASKNAME".out", "w", stdout);
}
cin >> n >> m;
b.assign(m + 1, 0);
p.assign(m + 1, 0);
for (int i = 1; i <= m; i ++)
cin >> b[i] >> p[i];
if (n <= 2000 && m <= 2000)
subtask123 :: main();
else
subtask4 :: main();
return 0;
}
Compilation message (stderr)
skyscraper.cpp: In function 'int main()':
skyscraper.cpp:103:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
103 | freopen (TASKNAME".inp", "r", stdin);
| ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
skyscraper.cpp:104:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
104 | freopen (TASKNAME".out", "w", stdout);
| ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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