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
using namespace std;
const int N = 3e4 + 69;
int n,m;
vector<int>V[N];
vector< pair<int,int> >gr[N];
int X[N],P[N],D[N];
set< pair<int,int> > s;
int main(){
cin>>n>>m;
for(int i=1;i<=m;i++){
cin>>X[i]>>P[i];
X[i]++;
V[X[i]].push_back(i);
}
for(int i=1;i<=m;i++){
if(i>1){
D[i] = 1e9;
s.insert({1e9,i});
}
}
D[1] = 0;
s.insert({0,1});
while(s.size()){
pair<int,int> p = *(s.begin());
s.erase(s.begin());
int i = p.second;
int dist = p.first;
for(int j=X[i];j<=n;j+=P[i]){
for(int k=0;k<V[j].size();k++){
int to = V[j][k];
if(D[to] > dist + (j-X[i])/P[i]){
s.erase({D[to],to});
D[to] = dist + (j-X[i])/P[i];
s.insert({D[to],to});
}
}
}
for(int j=X[i]-P[i];j>=1;j-=P[i]){
for(int k=0;k<V[j].size();k++){
int to = V[j][k];
if(D[to] > dist + (X[i]-j)/P[i]){
s.erase({D[to],to});
D[to] = dist + (X[i]-j)/P[i];
s.insert({D[to],to});
}
}
}
}
if(D[2]==1e9)
D[2] = -1;
cout<<D[2]<<endl;
}
Compilation message (stderr)
skyscraper.cpp: In function 'int main()':
skyscraper.cpp:48:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for(int k=0;k<V[j].size();k++){
~^~~~~~~~~~~~
skyscraper.cpp:61:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for(int k=0;k<V[j].size();k++){
~^~~~~~~~~~~~
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