BZOJ 4070: [Apio2015]雅加达的摩天楼

/**************************************************************
    Problem: 4070
    User: BeiYu
    Language: C++
    Result: Accepted
    Time:8152 ms
    Memory:175408 kb
****************************************************************/
 
#include <bits/stdc++.h>
using namespace std;
 
#define uor(i,j,k) for(int i=j;i<=(int)k;i++)
#define uep(i,j,k) for(int i=j;i<(int)k;i++)
 
inline int in(int x=0,char s=getchar()) { while(s>‘9‘||s<‘0‘)s=getchar();
    while(s>=‘0‘&&s<=‘9‘)x=x*10+s-‘0‘,s=getchar();return x; }
 
const int N = 30001;
const int B = 86;
const int NN = N*B+N;
const int M = N*B*5;
const int oo = 0x3f3f3f3f;
 
int n,m,ss,tt,pe;
int to[M],ww[M];
int nxt[M],hd[NN];
int d[NN];
bool b[NN];
 
int get_id(int x,int y) { return x*n+y; }
void AddEdge(int u,int v,int w) 
{ nxt[++pe]=hd[u],to[pe]=v,ww[pe]=w,hd[u]=pe; }
 
int SPFA(int s,int t) {
    memset(d,0x3f,sizeof(d));
    queue<int> q;q.push(s);
    d[s]=0,b[s]=1;
    for(int x;!q.empty();) {
        x=q.front(),q.pop(),b[x]=0;
        for(int i=hd[x];i;i=nxt[i]) {
            int v=to[i],w=ww[i];
            if(d[x]+w<d[v]) {
                d[v]=d[x]+w;
                if(!b[v]) q.push(v),b[v]=1;
            }
        }
    }return d[t]==oo?-1:d[t];
}
/*
void out() {
    for(int i=0;i<=(B+1)*n+n-1;i++) {
        cout<<i<<"-->";
        uep(j,0,g[i].size()) cout<<edge[g[i][j]].to<<" ";
        cout<<endl;
    }
}*/
int main() {
//  cout<<sizeof(to)*4/1024.0/1024.0<<endl;
    n=in(),m=in();
    uep(i,0,m) {
        int b=in(),p=in();
        if(i==0) ss=b;
        if(i==1) tt=b;
        if(p>B) {
            for(int j=1;j*p<n;j++) {
                if(b+j*p<n) AddEdge(b,b+j*p,j);
                if(b-j*p>=0) AddEdge(b,b-j*p,j);
            }
        } else {
            AddEdge(b,get_id(p,b),0);
        }
    }
    for(int i=1;i<=B;i++) for(int j=0;j<i;j++) for(int k=j+i;k<n;k+=i)
        AddEdge(get_id(i,k),get_id(i,k-i),1),AddEdge(get_id(i,k-i),get_id(i,k),1);
    for(int i=1;i<=B;i++) for(int j=0;j<i;j++) for(int k=j;k<n;k+=i)
        AddEdge(get_id(i,k),k,0);
     
//  out();
     
    printf("%d\n",SPFA(ss,tt));
    return 0;
}