new file: P1967.cpp

P1967.cpp

@@ -0,0 +1,128 @@
+#include <bits/stdc++.h>
+using namespace std;
+int n, m, q;
+int a[10005];
+vector<pair<int, pair<int, int>>> edge;
+vector<pair<int, int>> fri[10005];
+struct BCJ {
+    int fa[10005];
+    int find(int x) {
+        if (fa[x] == x) return x;
+        return fa[x] = find(fa[x]);
+    }
+} b;
+struct SEG {
+    int num[10005 * 4];
+    void init(int now, int nl, int nr) {
+        if (nl == nr) {
+            num[now] = a[nl];
+            return;
+        }
+        int mid = (nl + nr) >> 1;
+        init(now * 2, nl, mid);
+        init(now * 2 + 1, mid + 1, nr);
+        num[now] = min(num[now * 2], num[now * 2 + 1]);
+    }
+    int query(int now, int nl, int nr, int l, int r) {
+        if (nr < l || nl > r) return INT_MAX;
+        if (l <= nl && nr <= r) return num[now];
+        int mid = (nl + nr) >> 1;
+        return min(query(now * 2, nl, mid, l, r), query(now * 2 + 1, mid + 1, nr, l, r));
+    }
+} seg;
+int fa[10005];
+pair<int, int> son[10005];
+int cnt[10005];
+int top[10005];
+int dfn[10005];
+int dep[10005];
+int nowdfn;
+void dfs1(int now, int from) {
+    cnt[now] = 1;
+    for (auto i : fri[now]) {
+        int v = i.second;
+        int w = i.first;
+        if (v == from) continue;
+        fa[v] = now;
+        dep[v] = dep[now] + 1;
+        dfs1(v, now);
+        cnt[now] += cnt[v];
+        if (cnt[son[now].first] < cnt[v]) {
+            son[now].first = v;
+            son[now].second = w;
+        }
+    }
+}
+void dfs2(int now, int from, int w) {
+    dfn[now] = ++nowdfn;
+    top[now] = from;
+    a[dfn[now]] = w;
+    if (son[now].first) {
+        dfs2(son[now].first, from, son[now].second);
+    }
+    for (auto i : fri[now]) {
+        int v = i.second;
+        int ww = i.first;
+        if (v == fa[now] || v == son[now].first) continue;
+        dfs2(v, v, ww);
+    }
+}
+int pt(int x, int y) {
+    if (x == y) return INT_MAX;
+    int ans = INT_MAX;
+    while (top[x] != top[y]) {
+        if (dep[top[x]] < dep[top[y]]) swap(x, y);
+        ans = min(ans, seg.query(1, 1, n, dfn[top[x]], dfn[x]));
+        x = fa[top[x]];
+    }
+    if (dep[x] < dep[y]) swap(x, y);
+    if (dfn[y] + 1 <= dfn[x]) {
+        ans = min(ans, seg.query(1, 1, n, dfn[y] + 1, dfn[x]));
+    }
+    return ans;
+}
+int main() {
+    scanf("%d%d", &n, &m);
+    for (int i = 1; i <= n; ++i) {
+        b.fa[i] = i;
+    }
+    for (int i = 1, u, v, w; i <= m; ++i) {
+        scanf("%d%d%d", &u, &v, &w);
+        edge.push_back({w, {u, v}});
+    }
+    sort(edge.begin(), edge.end(),
+         [](const pair<int, pair<int, int>> &x,
+            const pair<int, pair<int, int>> &y) {
+             return x.first > y.first;
+         });
+    for (auto i : edge) {
+        int w = i.first;
+        int u = i.second.first;
+        int v = i.second.second;
+        if (b.find(u) != b.find(v)) {
+            fri[u].push_back({w, v});
+            fri[v].push_back({w, u});
+            b.fa[b.find(u)] = b.find(v);
+        }
+    }
+    for (int i = 1; i <= n; ++i) {
+        if (!dfn[i]) {
+            dfs1(i, 0);
+            dfs2(i, i, INT_MAX);
+        }
+    }
+    seg.init(1, 1, n);
+    scanf("%d", &q);
+    while (q--) {
+        int x, y;
+        scanf("%d%d", &x, &y);
+        if (b.find(x) != b.find(y)) {
+            printf("-1\n");
+            continue;
+        }
+        int ans = pt(x, y);
+        printf("%d\n", ans == INT_MAX ? -1 : ans);
+    }
+
+    return 0;
+}