POJ 3662 Telephone Lines
Source: USACO 2008 January Silver.1
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using namespace std;
const int N = 1001, M = 20002;
int n, m, k, u, v, ww, h[N], e[M], w[M], ne[M], idx, dist[N];
bool st[N];
void add(int u, int v, int ww) {
e[++idx] = v, w[idx] = ww, ne[idx] = h[u], h[u] = idx;
}
bool check(int bound) {
memset(dist, 0x3f, sizeof(dist));
memset(st, 0, sizeof(st));
dist[1] = 0;
deque<int> q;
q.push_back(1);
while (q.size()) {
int u = q.front(); q.pop_front();
if (st[u]) continue;
st[u] = true;
for (int i = h[u]; i; i = ne[i]) {
int v = e[i], d = w[i] > bound;
if (dist[v] > dist[u] + d) {
dist[v] = dist[u] + d;
if (!d) q.push_front(v);
else q.push_back(v);
}
}
}
return dist[n] <= k;
}
int main() {
scanf("%d%d%d", &n, &m, &k);
while (m--) {
scanf("%d%d%d", &u, &v, &ww);
add(u, v, ww), add(v, u, ww);
}
int l = 0, r = 1e6 + 1;
while (l < r) {
int mid = l + r >> 1;
if (check(mid)) r = mid;
else l = mid + 1;
}
if (r == 1e6 + 1) r = -1;
printf("%d\n", r);
return 0;
}