SPOJ——MST

Problem

Find the minimum spanning tree of the graph.

Input

On the first line there will be two integers N - the number of nodes and M - the number of edges. (1 <= N <= 10000), (1 <= M <= 100000)
M lines follow with three integers i j k on each line representing an edge between node i and j with weight k. The IDs of the nodes are between 1 and n inclusive. The weight of each edge will be <= 1000000.

Output

Single number representing the total weight of the minimum spanning tree on this graph. There will be only one possible MST.

Sample Input

4 5
1 2 10
2 3 15
1 3 5
4 2 2
4 3 40

Sample Output

17

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思路

最小生成树模板题，Prim就好，注意输出结果int会溢出，要开到long。

代码

#include
#include
#include
#define N 10005
#define INF 0x3f3f3f3f
using namespace std;
int cost[N][N];
int mincost[N];
bool used[N];
int V, E;
long Prim() {
    memset(mincost, 0x3f, sizeof(mincost));
    memset(used, 0, sizeof(used));
    mincost[0] = 0;
    long res = 0;
    while (1) {
        int v = -1;
        for (int u = 0; u < V; u++) {
            if (!used[u] && (v == -1 || mincost[u] < mincost[v]))v = u;
        }
        if (v == -1)break;
        used[v] = true;
        res += mincost[v];
        for (int u = 0; u < V; u++) {
            mincost[u] = min(mincost[u], cost[v][u]);
        }
    }
    return res;
}
int main() {
    int v1, v2, w;
    cin >> V >> E;
    memset(cost, 0x3f, sizeof(cost));
    for (int i = 0; i < E; i++) {
        cin >> v1 >> v2 >> w;
        cost[v1-1][v2-1] = w;
        cost[v2-1][v1-1] = w;
    }
    cout << Prim() << endl;
    return 0;
}