1864. [Zjoi2006]三色二叉树

https://hydro.ac/d/bzoj/record/6322eda9bdf9bc31d160a1ca

BZOJ/1864/1864.cpp

@@ -0,0 +1,94 @@
+#include <iostream>
+#include <algorithm>
+#include <cstring>
+#include <string>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 5e5 + 5;
+
+int n, p = 1, f1[N][3], f2[N][3];
+std::string s;
+std::vector<int> g[N];
+
+void dfs1(int fa) {
+    int t = s[p] - '0', u = p++;
+
+    if (fa) g[fa].push_back(u);
+    if (!t) return;
+
+    dfs1(u);
+    if (t == 2) dfs1(u);
+}
+
+void dfs2(int u) {
+    if (g[u].empty()) {
+        f1[u][0] = f2[u][0] = 1;
+        f1[u][1] = f1[u][2] = f2[u][1] = f2[u][2] = 0;
+
+        return;
+    }
+
+    for (int v : g[u]) {
+        dfs2(v);
+
+        f1[u][0] = std::max(f1[v][1], f1[v][2]) + 1;
+        f1[u][1] = std::max(f1[v][0], f1[v][2]);
+        f1[u][2] = std::max({f1[u][2], f1[v][0], f1[v][1]});
+        f2[u][0] = std::min({f2[u][0], f2[v][1] + 1, f2[v][2] + 1});
+        f2[u][1] = std::min({f2[u][1], f2[v][0], f2[v][2]});
+        f2[u][2] = std::min({f2[u][2], f2[v][0], f2[v][1]});
+    }
+
+    switch (g[u].size()) {
+        case 1: {
+            int v = g[u][0];
+
+            f1[u][0] = std::max(f1[v][1], f1[v][2]) + 1;
+            f1[u][1] = std::max(f1[v][0], f1[v][2]);
+            f1[u][2] = std::max(f1[v][0], f1[v][1]);
+
+            f2[u][0] = std::min(f2[v][1], f2[v][2]) + 1;
+            f2[u][1] = std::min(f2[v][0], f2[v][2]);
+            f2[u][2] = std::min(f2[v][0], f2[v][1]);
+
+            break;
+        }
+        case 2: {
+            int v1 = g[u][0],
+                v2 = g[u][1];
+
+            f1[u][0] = std::max(f1[v1][1] + f1[v2][2], f1[v1][2] + f1[v2][1]) + 1;
+            f1[u][1] = std::max(f1[v1][0] + f1[v2][2], f1[v1][2] + f1[v2][0]);
+            f1[u][2] = std::max(f1[v1][0] + f1[v2][1], f1[v1][1] + f1[v2][0]);
+
+            f2[u][0] = std::min(f2[v1][1] + f2[v2][2], f2[v1][2] + f2[v2][1]) + 1;
+            f2[u][1] = std::min(f2[v1][0] + f2[v2][2], f2[v1][2] + f2[v2][0]);
+            f2[u][2] = std::min(f2[v1][0] + f2[v2][1], f2[v1][1] + f2[v2][0]);
+
+            break;
+        }
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> s;
+    n = s.size();
+    s = ' ' + s;
+
+    dfs1(0);
+
+    memset(f2, 0x3f, sizeof(f2));
+
+    dfs2(1);
+
+    cout << std::max({f1[1][0], f1[1][1], f1[1][2]}) << ' ' << std::min({f2[1][0], f2[1][1], f2[1][2]}) << endl;
+
+    return 0;
+}