2533: solve in C++17

problem/2533/input

@@ -0,0 +1,8 @@
+8
+1 2
+1 3
+1 4
+2 5
+2 6
+4 7
+4 8

problem/2533/input2

@@ -0,0 +1,9 @@
+9
+1 2
+1 3
+2 4
+3 5
+3 6
+4 7
+4 8
+4 9

problem/2533/main.cpp

@@ -0,0 +1,81 @@
+#include <algorithm>
+#include <iostream>
+#include <queue>
+#include <vector>
+
+using namespace std;
+
+int N;
+vector<vector<int>> ADJ;
+vector<pair<int, int>> depths;
+vector<int> leaves;
+vector<int> parents;
+vector<bool> early;
+
+void dfs(int u, int s, int depth) {
+    depths.emplace_back(-depth, u);
+    bool has_child = false;
+    for (auto v : ADJ[u]) {
+        if (v == s) {
+            continue;
+        }
+        has_child = true;
+        parents[v] = u;
+        dfs(v, u, depth + 1);
+    }
+    if (!has_child) {
+        leaves.emplace_back(u);
+    }
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cin >> N;
+    ADJ.resize(N);
+    parents.resize(N);
+    early.resize(N);
+    for (int i = 0; i < N - 1; i++) {
+        int u, v;
+        cin >> u >> v;
+        ADJ[u - 1].emplace_back(v - 1);
+        ADJ[v - 1].emplace_back(u - 1);
+    }
+    parents[0] = -1;
+    dfs(0, -1, 0);
+    int ans = 0;
+    for (auto leaf : leaves) {
+        if (!early[parents[leaf]]) {
+            early[parents[leaf]] = true;
+            ans++;
+        }
+    }
+    sort(depths.begin(), depths.end());
+    for (auto [depth, u] : depths) {
+        if (early[u]) {
+            continue;
+        }
+        int parent = parents[u];
+        bool all_early = true;
+        for (auto v : ADJ[u]) {
+            if (v == parent) {
+                continue;
+            }
+            if (!early[v]) {
+                all_early = false;
+                break;
+            }
+        }
+        if (all_early) {
+            if (parent != -1 && !early[parent]) {
+                early[parent] = true;
+                ans++;
+            }
+        } else {
+            early[u] = true;
+            ans++;
+        }
+    }
+    cout << ans << "\n";
+    return 0;
+}

problem/2533/output

@@ -0,0 +1 @@
+3

problem/2533/output2

@@ -0,0 +1 @@
+3