whust 2016 warm up E ||codeforces 689 B. Mike and Shortcuts (spfa)

2016-07-18 · 2 min read · spfa 最短路

cf689B题目链接

题意：n点。。点i到点j的代价是|i-j|..给出n条近路。。。a[i]表示点i到a[i]的代价为1（注意近路不一定就近）

思路：一开始建边卡了一下。。。实际上只要连相邻的就好了。。。然后边表只开了2N蠢哭。。。实际上应该3M...因为连相邻的边是双向的。。。再加上近路的单向。。。然后spfa就好了。。。。

/* ***********************************************
Author :111qqz
Created Time :2016年07月18日 星期一 13时33分18秒
File Name :code/2016whust/F.cpp
************************************************ */

 1#include <cstdio>
 2#include <cstring>
 3#include <iostream>
 4#include <algorithm>
 5#include <vector>
 6#include <queue>
 7#include <set>
 8#include <map>
 9#include <string>
10#include <cmath>
11#include <cstdlib>
12#include <ctime>
13#define fst first
14#define sec second
15#define lson l,m,rt<<1
16#define rson m+1,r,rt<<1|1
17#define ms(a,x) memset(a,x,sizeof(a))
18typedef long long LL;
19#define pi pair < int ,int >
20#define MP make_pair

 1using namespace std;
 2const double eps = 1E-8;
 3const int dx4[4]={1,0,0,-1};
 4const int dy4[4]={0,-1,1,0};
 5const int inf = 0x3f3f3f3f;
 6const int N=2E5+7;
 7int n;
 8int a[N];
 9bool inq[N];
10int d[N];
11int head[N];
12int cnt;

1struct Edge
2{
3    int v;
4    int w;
5    int nxt;
6}edge[8*N];

 1void addedge( int u,int v,int w)
 2{
 3    edge[cnt].v = v;
 4    edge[cnt].w = w;
 5    edge[cnt].nxt = head[u];
 6    head[u] = cnt;
 7    cnt++;
 8}
 9void init()
10{
11    ms(head,-1);
12    cnt = 0 ;
13}
14void spfa( int s)
15{
16    ms(inq,false);
17    ms(d,0x3f);
18    queue<int>q;
19    q.push(s);
20    inq[s] = true;
21    d[s] =  0;

1    while (!q.empty())
2    {
3	int u = q.front();
4//<	cout<<"u:"<<u<<endl;
5	q.pop();
6	inq[u] = false;

 1	for ( int i = head[u] ; i!=-1 ; i = edge[i].nxt)
 2	{
 3	    int v = edge[i].v;
 4	    int w = edge[i].w;
 5	    if (d[v]>d[u]+w)
 6	    {
 7		d[v] = d[u] + w;
 8		if (inq[v]) continue;
 9		inq[v] = true;
10		q.push(v);
11	    }
12//	    if (a[u]==v&&d[v]>1)
13//	    {
14//		d[v] = 1;
15//		if (inq[v]) continue;
16//		inq[v] = true;
17//		q.push(v);
18//	    }

1	}
2    }
3}
4int main()
5{
6	#ifndef  ONLINE_JUDGE 
7	freopen("code/in.txt","r",stdin);
8  #endif

 1	cin>>n;
 2	init();
 3	for ( int i = 1 ; i <= n ; i++)
 4	{
 5	    scanf("%d",&a[i]);
 6	    if (a[i]!=i)
 7	    addedge(i,a[i],1);
 8//	    addedge(1,i,i-1);
 9//	    addedge(i,1,i-1);
10//	    else addedge(i,a[i],0);
11	}
12	for ( int i = 1;  i <= n-1 ; i++)
13	{
14	    addedge(i,i+1,1);
15	    addedge(i+1,i,1);
16	}

	spfa(1);

	for ( int i = 1 ; i <= n ; i++) printf("%d ",d[i]);

1  #ifndef ONLINE_JUDGE  
2  fclose(stdin);
3  #endif
4    return 0;
5}