POJ 2607 Fire Station

又是一道最短路的题，为了提高效率，我用的邻接链表+SPFA做的，速度很快，0ms过的。

首先，初始化完dist数组后，对每个消防站作为起点都求一次最短路，期间不再初始化dist数组，这样最后得到的dist数组就是每个居民到最近的消防站的距离。

然后枚举每个点，每次求一下最短路，用其中的最大值比较一下。 然后这个代码贴到zoj上是过不了的，因为那里的输入很恶心人。还有空行神马的。

/*ID: sdj22251PROG: subsetLANG: C++*/#include <iostream>#include <vector>#include <list>#include <map>#include <set>#include <deque>#include <queue>#include <stack>#include <bitset>#include <algorithm>#include <functional>#include <numeric>#include <utility>#include <sstream>#include <iomanip>#include <cstdio>#include <cmath>#include <cstdlib>#include <cctype>#include <map>#include <string>#include <cstring>#include <cmath>#include <ctime>#define LOCA#define MAXN 505#define INF 0x0fffffff#define eps 1e-7using namespace std;struct node{    int v, w;    node *next;} edge[MAXN];int d[MAXN], dd[MAXN], n, m, fire[MAXN];int q[MAXN * 3];bool visited[MAXN];void spfa(int src, int *ecost){    int h, t, u, i;    node *ptr;    h = 0, t = 1;    memset(visited, 0, sizeof(visited));    q[0] = src;    ecost[src] = 0;    visited[src] = true;    while(h < t)    {        u = q[h++];        visited[u] = false;        ptr = edge[u].next;        while(ptr)        {            if(ecost[ptr -> v] > ecost[u] + ptr -> w)            {                ecost[ptr -> v] = ecost[u] + ptr -> w;                if(!visited[ptr -> v])                {                    q[t++] = ptr -> v;                    visited[ptr -> v] = true;                }            }            ptr = ptr -> next;        }    }}void insert(const int &x, const int &y, const int &w){    node *ptr = new node;    ptr -> v = y;    ptr -> w = w;    ptr -> next = edge[x].next;    edge[x].next = ptr;}int main(){#ifdef LOCAL    freopen("d:/data.in","r",stdin);    freopen("d:/data.out","w",stdout);#endif    char s[140];    int i, u, v, w, j;    while(scanf("%d%d", &m, &n) != EOF)    {        for(i = 0; i < m; i++)        {            scanf("%d", &fire[i]);        }        int mi = INF;        int ans = 1;        for(i = 0; i <= n; i++)        {            edge[i].next = NULL;        }        while(scanf("%d%d%d", &u, &v, &w) != EOF)        {            insert(u, v, w);            insert(v, u, w);        }        for(i = 0; i <= n; i++)            d[i] = INF;        for(i = 0; i < m; i++)            spfa(fire[i], d);        for(i = 1; i <= n; i++)        {            int mx = 0;            if(d[i] == 0) continue;            for(j = 0; j <= n; j++)                dd[j] = d[j];            spfa(i, dd);            for(j = 1; j <= n; j++)                mx = max(mx, dd[j]);            if(mi > mx)            {                mi = mx;                ans = i;            }        }        printf("%d\n", ans);    }    return 0;}