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| #include <bits/stdc++.h>
using namespace std;
const int iol = 1024 * 1024;
char buf[iol], *ioh, *iot, ioc;
bool iosig;
inline char read() {
if (ioh == iot) {
iot = (ioh = buf) + fread(buf, 1, iol, stdin);
if (ioh == iot) return -1;
}
return *ioh++;
}
template<class T>
inline bool read(T &x) {
iosig = false;
for (ioc = read(); !isdigit(ioc); ioc = read()) {
if (ioc == -1) return false;
if (ioc == '-') iosig = true;
}
x = 0;
while (ioc == '0') ioc = read();
for (; isdigit(ioc); ioc = read())
x = (x << 1) + (x << 3) + (ioc ^ '0');
ioh--;
if (iosig) x = -x;
return true;
}
struct DisjointSet {
int *rank, *father, size;
inline int get(int x) {
register int p = x, i;
while (p != father[p]) p = father[p];
while (x != p) i = father[x], father[x] = p, x = i;
return p;
}
inline void put(int x, int y) {
x = get(x), y = get(y);
if (rank[x] > rank[y]) father[y] = x;
else {
father[x] = y;
if (rank[x] == rank[y]) rank[y]++;
}
}
inline void init(int x) {
rank[x] = 0, father[x] = x;
}
DisjointSet(int n) : rank(new int[n + 1]), father(new int[n + 1]), size(n + 1) {
for (register int i = 1; i <= n; i++)
father[i] = i;
}
} *s;
int n, m;
#define INF 0x3fffffff
const int MAX = 100000 + 50;
struct Node {
int v;
long long w;
Node() {}
Node(int v0, long long w0) : v(v0), w(w0) {}
inline bool operator < (const Node &b) const {
return w < b.w;
}
};
bool vis[MAX], toPush[MAX];
vector<Node> edge[MAX];
long long dis[MAX];
inline void spfa() {
queue<int> q;
memset(dis, 127, sizeof(dis));
memset(vis, false, sizeof(vis));
for (register int i = 1; i <= n; i++)
if (toPush[i])
q.push(i), vis[i] = true, dis[i] = 0;
while (!q.empty()) {
int now = q.front();
q.pop();
vis[now] = false;
for (int i = 0; i < edge[now].size(); ++i) {
Node *x = &edge[now][i];
if (dis[x->v] > dis[now] + x->w) {
dis[x->v] = dis[now] + x->w;
if (!vis[x->v]) vis[x->v] = true, q.push(x->v);
}
}
}
}
inline void addEdge(int u, int v, int w) {
edge[u].push_back(Node(v, w));
edge[v].push_back(Node(u, w));
}
inline void init() {
read(n), read(m);
for (register int i = 1; i <= n; i++)
read(toPush[i]);
for (register int i = 1, u, v, w; i <= m; i++)
read(u), read(v), read(w), addEdge(u, v, w);
spfa();
}
struct data {
int u, v;
long long w;
inline bool operator < (const data &b) const {
return w < b.w;
}
} d[400000 + 20];
int cnt;
long long ans;
inline void solve() {
for (register int i = 1; i <= n; i++) {
if (!toPush[i]) {
for (register int j = 0; j < edge[i].size(); j++) {
Node *e = &edge[i][j];
if (dis[e->v] + e->w == dis[i])
d[++cnt].u = e->v, d[cnt].v = i, d[cnt].w = e->w;
}
}
}
s = new DisjointSet(n + 1);
register int k = 0;
for (register int i = 1; i <= n; i++)
if (toPush[i])
s->put(i, n + 1), k++;
sort(d + 1, d + 1 + cnt);
for (register int i = 1; i <= cnt; i++) {
if (s->get(d[i].u) != s->get(d[i].v)) {
s->put(d[i].u, d[i].v);
k++, ans += d[i].w;
if (k == n) break;
}
}
if (k != n) cout << "impossible";
else cout << ans;
}
int main() {
init();
solve();
return 0;
}
|
