POJ_3013_Big Christmas Tree

这道题目TLE了好多次才过，有些点要注意的：

1.图是无向图来的

2.边数组要开10W以上

3.求最短路时，保存中间路径长度要用long long，当然结果也就是long long保存啦

4.当0==n或1==n，输出0，当0==m，输出No Answer;

5.INF要大一点，可以用0x7f7f7f7f7f7f7f7fLL;

参考代码(spfa)：

#include <stdio.h>#include <stdlib.h>#include <string.h>typedef struct Edge {    int to,next;    int dis;}Edge;const int MAXN = 200100;const int MAXM = MAXN << 1;const long long INF = 0x7f7f7f7f7f7f7f7fLL;bool vis[MAXN];Edge edge[MAXN];Edge head[MAXN];long long dis[MAXN];int val[MAXN];int queue[MAXM];int total,n,m;void init();void add_edge(int from,int to,int dis);void spfa(int src);int main(int argc,char * argv[]) {    int i,j,k;    int x,y,z;    int Case,flag;    long long ans;    scanf("%d",&Case);    while (Case-->0) {        scanf("%d%d",&n,&m);        init();        for (i=1;i<=n;++i) scanf("%d",val+i);        for (i=1;i<=m;++i) {            scanf("%d%d%d",&x,&y,&z);            add_edge(x,y,z);            add_edge(y,x,z);        }        if (0 == n || 1 == n) {            printf("0\n");            continue;           }        if (0 == m) {            printf("No Answer\n");            continue;        }        spfa(1);        flag = 1;        ans = 0LL;        for (i=2;i<=n;++i) {            if (INF == dis[i]) {                flag = 0;                break;            }            ans += dis[i] * val[i];        }        if (!flag) {            printf("No Answer\n");        } else {            printf("%lld\n",ans);        }    }    return 0;}void spfa(int src) {    int p,num;    int front,tail,cur;    memset(dis,0x7f,sizeof(dis));    memset(vis,0,sizeof(vis));    dis[src] = 0;    vis[src] = 1;    tail = 0;    front = -1;    queue[0] = src;    while (front != tail) {        ++front;        if (front >= MAXM) front = 0;        cur = queue[front];        p = head[cur].next;        while (p) {            if (-1 == dis[edge[p].to] || dis[edge[p].to] - edge[p].dis > dis[cur]) {                dis[edge[p].to] = dis[cur] + edge[p].dis;                if (!vis[edge[p].to]) {                    vis[edge[p].to] = 1;                    ++tail;                    if (tail >= MAXM) tail = 0;                    queue[tail] = edge[p].to;                }            }            vis[cur] = 0;            p = edge[p].next;        }    }            }void init() {    total = 0;    for (int i=0;i<=n;++i)        head[i].next = 0;}void add_edge(int from,int to,int dis) {    ++total;    edge[total].to = to;    edge[total].dis = dis;    edge[total].next = head[from].next;    head[from].next = total;}

参考代码(dijkstra+priority_queue)：

#include <stdio.h>#include <stdlib.h>#include <string.h>#include <queue>using namespace std;typedef struct Edge {    int to,next;    int dis;}Edge;typedef struct Node {    int from;    long long dis;    Node(){};    Node(int f,long long d):from(f),dis(d){};}Node;const int MAXN = 200100;const long long INF = 0x7f7f7f7f7f7f7f7fLL;bool vis[MAXN];Edge edge[MAXN];Edge head[MAXN];long long dis[MAXN];int val[MAXN];int total,n,m;void init();void add_edge(int from,int to,int dis);void dijkstra(int src);bool operator < (const Node &a,const Node &b);int main(int argc,char * argv[]) {    int i,j,k;    int x,y,z;    int Case,flag;    long long ans;    scanf("%d",&Case);    while (Case-->0) {        scanf("%d%d",&n,&m);        init();        for (i=1;i<=n;++i) scanf("%d",val+i);        for (i=1;i<=m;++i) {            scanf("%d%d%d",&x,&y,&z);            add_edge(x,y,z);            add_edge(y,x,z);        }        if (0 == n || 1 == n) {            printf("0\n");            continue;           }        if (0 == m) {            printf("No Answer\n");            continue;        }        dijkstra(1);        flag = 1;        ans = 0LL;        for (i=2;i<=n;++i) {            if (INF == dis[i]) {                flag = 0;                break;            }            ans += dis[i] * val[i];        }        if (!flag) {            printf("No Answer\n");        } else {            printf("%lld\n",ans);        }    }    return 0;}void dijkstra(int src) {    int p;    Node cur;    priority_queue<Node> pq;    memset(vis,0,sizeof(vis));    memset(dis,0x7f,sizeof(dis));    dis[src] = 0;    while (!pq.empty()) pq.pop();    pq.push(Node(src,0));    while (!pq.empty()) {        cur = pq.top();        pq.pop();        if (vis[cur.from]) continue;        vis[cur.from] = 1;        p = head[cur.from].next;        while (p) {            if (dis[edge[p].to] - edge[p].dis > dis[cur.from]) {                dis[edge[p].to] = dis[cur.from] + edge[p].dis;                pq.push(Node(edge[p].to,dis[edge[p].to]));            }            p = edge[p].next;        }    }}void init() {    total = 0;    for (int i=0;i<=n;++i)        head[i].next = 0;}void add_edge(int from,int to,int dis) {    ++total;    edge[total].to = to;    edge[total].dis = dis;    edge[total].next = head[from].next;    head[from].next = total;}bool operator < (const Node &a,const Node &b) {    return a.dis > b.dis;}