CCF-交通规划-dijkstra+贪心

 1 #include <iostream>
 2 #include <queue>
 3 #include <vector>
 4 
 5 #define NMAX 10005
 6 #define INTMAX 0x7fffffff
 7 
 8 using namespace std;
 9 
10 // v表示节点，cost表示出发点到v点的距离
11 struct Node {
12     int v; 
13     int cost;
14     Node(int vv = 0, int c = 0) {
15         v = vv, cost = c;
16     }
17     // 优先队列将按距离从小到大排列
18     friend bool operator<(Node n1, Node n2) {
19         return n1.cost > n2.cost;
20     }
21 };
22 
23 // v表示边的另一端节点，cost表示该边的权重
24 struct Edge {
25     int v;
26     int cost;
27     Edge(int vv = 0, int c = 0) {
28         v = vv, cost = c;
29     }
30 };
31 
32 vector<Edge>G[NMAX];    // 无向图
33 bool marked[NMAX];      // D算法中每个顶点仅处理一遍
34 int disto[NMAX];        // 出发点到某点距离
35 int costo[NMAX];        // 接通该点需要增加的边的权重
36 int N, M;
37 
38 void dijkstra(int s) {
39     for (int i = 0; i <= N; i++) {
40         costo[i] = disto[i] = INTMAX;//初始化 
41         marked[i] = false;
42     }
43     disto[s] = 0;
44     costo[s] = 0;
45     priority_queue<Node>pq;     // 保存<v,disto[v]>且按disto[v]升序排列
46     pq.push(Node(s, 0));
47     marked[0]=true;
48 
49     Node tmp;
50     while (!pq.empty()) {
51         tmp = pq.top();
52         pq.pop();
53         int v = tmp.v;
54         if (!marked[v]) {
55             marked[v]=true;
56             int len = G[v].size();
57             for (int i = 0; i < len; i++) {
58                 int vv = G[v][i].v;
59                 if(marked[vv])
60                     continue;
61                 int cost = G[v][i].cost;
62                 int newdist = disto[v] + cost;
63                 if (disto[vv] > newdist) {
64                     disto[vv] = newdist;
65                     costo[vv] = cost;   // 增加的内容
66                     pq.push(Node(vv, disto[vv]));
67                 }
68                 // 加入点vv时若出现多种距离相同的方案，选取新边最小那个
69                 if (disto[vv] == newdist) {
70                     costo[vv] = min(costo[vv], cost);
71                 }
72             }
73         }
74     }
75 }
76 
77 int main(void) {
78     cin >> N >> M;
79 
80     int s, e, c;
81     for (int i = 0; i < M; i++) {
82         cin >> s >> e >> c;
83         G[s].push_back(Edge(e, c));//无线图中添加边 
84         G[e].push_back(Edge(s, c));
85     }
86     dijkstra(1);
87 
88     // 统计边权重
89     int res = 0;
90     for (int i = 2; i <= N; i++) {
91         res += costo[i];
92     }
93     cout << res << endl;
94 
95     return 0;
96 }