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