Poj Jungle Road (优先队列Prim算法) 解题报告

题目链接：http://dsalgo.openjudge.cn/graph/2/
最小生成树算法，这是我第一次用优先队列实现Prim算法，记录一下
裸奔版

#include <iostream>#include <queue>using namespace std;const int MAXN = 30;const int INF = 1 << 20;int lowest[MAXN]; //各节点到已有生成树的最短距离，//树中节点为-1int roads[MAXN][MAXN];void initialize(int n){    for(int i = 0; i < n; ++i)        lowest[i] = INF;    for(int i = 0; i < n; ++i)    {        for(int j = 0; j < n; ++j)        {            roads[i][j] = INF;        }        roads[i][i] = 0;    }}int prim(int n){    int ret = 0;    int i, j, k;    lowest[0] = -1;    for(i = 1; i < n; ++i)    {        lowest[i] = roads[0][i];    }    for(i = 1; i < n; ++i) //每一轮迭代加入一个节点    {        int min = INF;        for(k = 0; k < n; ++k)        {            if(lowest[k] != -1 && lowest[k] < min)            {                min = lowest[k];                j = k;            }        }        ret += min;        lowest[j] = -1;        for(k = 0; k < n; ++k)        {            if(roads[j][k] < lowest[k]) lowest[k] = roads[j][k];        }    }    return ret;}int main(){    std::ios::sync_with_stdio(false);    std::cin.tie(0);    int n, numOfFrom, weight;    char village, from;    while(cin >> n && n != 0) {        initialize(n);        for(int i = 0; i < n-1; ++i)        {            cin >> village >> numOfFrom;            for(int j = 0; j < numOfFrom; ++j)            {                cin >> from >> weight;                roads[village-'A'][from-'A'] = weight;                 roads[from-'A'][village-'A'] = weight;             }         }        cout << prim(n) << endl;    }    return 0;}

优先队列版

#include <iostream>#include <queue>#include <vector>#include <cstring>using namespace std;const int MAXN = 30;const int INF = 1 << 20;struct Edge{    int sta, end, weight;    Edge(int s = 0, int e = 0, int w = INF):    sta(s), end(e), weight(w){}};bool operator < (const Edge & l, const Edge & r){ return l.weight > r.weight; }vector<Edge> nodesEdge[MAXN];void initialize(int n){    for(int i = 0; i < n; ++i)    {        nodesEdge[i].clear();    }}int prim(int n){    int total, ret = 0, sta;    bool visit[n];    memset(visit, 0, sizeof(visit));    priority_queue<Edge> que;    total = 1;    visit[0] = true;    sta = 0;    while(total < n) {        for(auto e : nodesEdge[sta])        {            if(!visit[e.end])            {                que.push(e);            }        }           //注意会有多个副本存在队列里面，未曾访问过的才是能用的        while(!que.empty() && visit[que.top().end]) {            que.pop();        }        sta = que.top().end;        ret += que.top().weight;        visit[que.top().end] = true;        que.pop();        ++total;    }    return ret;}int main(){    std::ios::sync_with_stdio(false);    std::cin.tie(0);    int n, numOfFrom, weight;    char village, from;    while(cin >> n && n != 0) {        initialize(n);        for(int i = 0; i < n-1; ++i)        {            cin >> village >> numOfFrom;            for(int j = 0; j < numOfFrom; ++j)            {                cin >> from >> weight;                nodesEdge[village-'A'].push_back(Edge(village-'A', from-'A', weight));                 nodesEdge[from-'A'].push_back(Edge(from-'A', village-'A', weight));             }         }        cout << prim(n) << endl;    }    return 0;}