BZOJ 2834: 回家的路 分层图最短路

2834: 回家的路

Time Limit: 10 Sec  Memory Limit: 128 MB
Submit: 125  Solved: 70
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Description

Input

Output

Sample Input

2 1
1 2
1 1 2 2

Sample Output

5

HINT

N<=20000,M<=100000

不会。。。翻题解

哇，分层图

感觉思路还是蛮精巧的：

把图拆成横纵两层

#include<cmath>#include<ctime>#include<cstdio>#include<cstring>#include<cstdlib>#include<complex>#include<iostream>#include<algorithm>#include<iomanip>#include<vector>#include<string>#include<bitset>#include<queue>#include<map>#include<set>using namespace std;inline int read(){int x=0,f=1;char ch=getchar();while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}while(ch<='9'&&ch>='0'){x=(x<<3)+(x<<1)+ch-'0';ch=getchar();}return x*f;}const int inf=0X7f7f7f7f;const int N=200100;const int M=5001000;int n,m,ecnt,last[N];struct EDGE{int to,nt,val;}e[M];inline void add(int u,int v,int val){e[++ecnt]=(EDGE){v,last[u],val};last[u]=ecnt;}struct node{int x,y,id;}a[N];inline bool cmp1(node x,node y){return x.x==y.x?x.y<y.y:x.x<y.x;}inline bool cmp2(node x,node y){return x.y==y.y?x.x<y.x:x.y<y.y;}int q[N],dis[N],s,t;bool inq[N];void spfa(){memset(dis,0X7f,sizeof(dis));dis[s]=0;int head=0,tail=1;q[0]=s;inq[s]=1;while(head!=tail){int u=q[head++];head%=N;inq[u]=0;for(int i=last[u];i;i=e[i].nt)if(dis[e[i].to]>dis[u]+e[i].val){dis[e[i].to]=dis[u]+e[i].val;if(!inq[e[i].to]){q[tail++]=e[i].to;inq[e[i].to]=1;tail%=N;}}}if(dis[t]>=inf)dis[t]=-1;}int main(){n=read();m=read();int x,y;s=m+1;t=m+2;for(int i=1;i<=m+2;i++){a[i].x=read();a[i].y=read();a[i].id=i;}sort(a+1,a+m+3,cmp1);for(int i=1;i<=m+2;i++)if(a[i].x==a[i+1].x)add(a[i].id,a[i+1].id,2*(a[i+1].y-a[i].y)),add(a[i+1].id,a[i].id,2*(a[i+1].y-a[i].y));sort(a+1,a+m+3,cmp2);for(int i=1;i<=m+2;i++)if(a[i].y==a[i+1].y)add(a[i].id+m+2,a[i+1].id+m+2,2*(a[i+1].x-a[i].x)),add(a[i+1].id+m+2,a[i].id+m+2,2*(a[i+1].x-a[i].x));for(int i=1;i<=m;i++)add(i,i+m+2,1),add(i+m+2,i,1);for(int i=m+1;i<=m+2;i++)add(i,i+m+2,0),add(i+m+2,i,0);spfa();printf("%d\n",dis[t]);return 0;}/*2 11 21 1 2 25*/