#1687. 【2022.10.24 联考】涂色

https://sjzezoj.com/submission/61769

S2OJ/1687/1687.cpp

@@ -0,0 +1,114 @@
+#include <iostream>
+#include <algorithm>
+#include <set>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 2e5 + 5;
+
+int n, k, a[N], c[N];
+int cnt, id[N], fa[N], dep[N], siz[N], son[N], top[N];
+std::vector<int> g[N], color[N];
+std::set<int> ans;
+
+void dfs1(int u, int f) {
+    siz[u] = 1;
+    fa[u] = f;
+    dep[u] = dep[f] + 1;
+
+    for (int v : g[u]) {
+        if (v == f) continue;
+
+        dfs1(v, u);
+        siz[u] += siz[v];
+        if (siz[v] > siz[son[u]]) son[u] = v;
+    }
+}
+
+void dfs2(int u, int t) {
+    id[u] = ++cnt;
+    top[u] = t;
+
+    if (!son[u]) return;
+    dfs2(son[u], t);
+
+    for (int v : g[u]) {
+        if (v == fa[u] || v == son[u]) continue;
+        dfs2(v, v);
+    }
+}
+
+int lca(int u, int v) {
+    while (top[u] != top[v]) {
+        if (dep[top[u]] < dep[top[v]]) std::swap(u, v);
+        u = fa[top[u]];
+    }
+
+    return dep[u] < dep[v] ? u : v;
+}
+
+void dfs3(int u, int f) {
+    for (int v : g[u]) {
+        if (v == f) continue;
+        dfs3(v, u);
+        c[u] += c[v];
+    }
+
+    if (c[u] == 1) ans.emplace(a[u]);
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> k;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+
+        color[a[i]].emplace_back(i);
+    }
+
+    for (int i = 1, x, y; i < n; i++) {
+        cin >> x >> y;
+
+        g[x].emplace_back(y);
+        g[y].emplace_back(x);
+    }
+
+    dfs1(1, 0);
+    dfs2(1, 1);
+
+    for (int i = 1; i <= k; i++) {
+        std::sort(color[i].begin(), color[i].end(), [&](int x, int y) -> bool { return id[x] < id[y]; });
+
+        int u = 0, p = 0;
+
+        for (int v : color[i]) {
+            if (!u) {
+                u = p = v;
+                c[v]++;
+            } else {
+                p = lca(u, v);
+                c[v]++, c[p]--;
+            }
+        }
+
+        c[fa[p]]--;
+    }
+
+    dfs3(1, 0);
+
+    cout << ans.size() << endl;
+
+    for (int x : ans) {
+        cout << x << ' ';
+    }
+
+    cout << endl;
+
+    return 0;
+}