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prims algorithm.cpp
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prims algorithm.cpp
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//Shafayet er Blog
//Prim's Algorithm
//Minimum spanning tree
#include <bits//stdc++.h>
using namespace std;
struct data {
int u, v, cost;
data (int a, int b, int c) {u = a; v = b; cost = c;}
bool operator < (const data &p) const {
return p.cost < cost;
}
};
bool visit[1010];
vector <int > G[1010];
vector <int > cost[1010];
int prims_mst (int n, int m, int k) {
priority_queue <data> pq;
memset (visit, 0, sizeof (visit));
visit[k] = 1;
for (int i = 0; i < G[k].size(); i++) {
int v = G[k][i];
int w = cost[k][i];
pq.push(data(k, v, w));
}
int cnt = 0;
while (pq.empty() == 0) {
data a = pq.top(); pq.pop();
int u, v, w;
u = a.u; v = a.v; w = a.cost;
//printf ("%d %d %d\n", u, v, w);
if (!visit[v]) {
visit[v] = 1;
cnt += w;
u = v;
for (int i = 0; i < G[u].size(); i++) {
v = G[u][i];
w = cost[u][i];
if (!visit[v]) pq.push(data(u, v, w));
}
}
}
return cnt;
}
int main ()
{
int n, e, temp = 0, tc, cas = 0, k, m;
//freopen ("in.txt", "r", stdin);
scanf (" %d", &tc);
while (tc--) {
scanf (" %d %d %d", &n, &m, &k);
for (int i = 0; i < m; i++) {
int u, v, w;
scanf (" %d %d %d", &u, &v, &w);
G[u].push_back (v);
G[v].push_back (u);
cost[u].push_back (w);
cost[v].push_back (w);
}
int x = prims_mst (n, m, k);
if (x == 0) printf ("Case %d: impossible\n", ++cas);
else printf ("Case %d: %d\n", ++cas, x);
vector <int> t1[1010];
vector <int> t2[1010];
swap (G, t1);
swap (cost, t2);
}
return 0;
}
/*
1
7 11 1
1 2 7
1 4 5
2 3 8
2 4 9
2 5 7
3 5 5
4 5 15
4 6 6
5 6 8
5 7 9
6 7 11
*/
/*
tricky case by jane alam jan..
1
5 10 3
3 1 80
3 2 67
3 4 94
1 2 39
1 0 53
1 4 16
2 1 88
2 0 30
2 4 47
4 1 26
*/