update

src/P4186/P4186.cpp

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+#include <algorithm>
+#include <cstdint>
+#include <iostream>
+#include <istream>
+#include <limits>
+#include <vector>
+
+using ll = int64_t;
+using std::cin, std::cout;
+
+const ll maxn = 1e5+5;
+ll n, k, dpts[maxn], rds[maxn], ans;
+std::vector<ll> edgs[maxn];
+
+void initdepth(const ll &fth, const ll &now){
+    dpts[now]=dpts[fth]+1;
+    for(const ll &nxt:edgs[now]){
+        if(nxt==fth)continue;
+        initdepth(now, nxt);
+    }
+}
+
+void initrd(const ll &fth, const ll &now){
+    if(edgs[now].size()==1)rds[now]=1;
+    for(const ll &nxt:edgs[now]){
+        if(nxt==fth)continue;
+        initrd(now, nxt);
+        rds[now]=std::min(rds[now], rds[nxt]+1);
+    }
+}
+
+void dfs(const ll &fth, const ll &now){
+    if(rds[now]<=dpts[now]){
+        ++ans;
+        return;
+    }
+    if(edgs[now].size()==1){
+        ++ans;
+        return;
+    }
+    for(const ll &nxt: edgs[now]){
+        if(nxt==fth)continue;
+        dfs(now, nxt);
+    }
+}
+
+int main(){
+    std::iostream::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
+    cin>>n>>k;
+    std::fill(rds, rds+1+n, std::numeric_limits<unsigned int>::max());
+    
+    for(ll i{1};i<n;i++){
+        ll u, v;
+        cin>>u>>v;
+        edgs[u].push_back(v);
+        edgs[v].push_back(u);
+    }
+    initdepth(0, k);
+    initrd(0, k);
+    dfs(0, k);
+    cout<<ans<<'\n';
+}