This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include<bits/stdc++.h>
#define ll long long
#define ff first
#define ss second
#define pb push_back
using namespace std;
const int N = 1e6 + 6;
bool is_dynamite[N];
int closest_explotion[N];
int furthest_dynamite[N];
int P[N],depth[N];
vector<int>gr[N];
int n,m;
void dfs(int x, int p){
depth[x] = depth[p] + 1;
P[x] = p;
for(int to : gr[x]){
if(to == p) continue;
dfs(to,x);
}
}
bool check(int k){
priority_queue<pair<int,int>>q;
int cnt_dynamites = 0;
for(int i = 1; i <= n; i++){
q.push({depth[i],i});
closest_explotion[i] = 1e9;
furthest_dynamite[i] = is_dynamite[i] ? 0 : -1;
}
while(q.size()){
auto pa = q.top();
q.pop();
int x = pa.second;
int p = P[x];
if(furthest_dynamite[x] == k){
cnt_dynamites++;
if(cnt_dynamites > m) return false;
closest_explotion[p] = 1;
} else {
if(closest_explotion[x] + furthest_dynamite[x] <= k){
closest_explotion[p] = min(closest_explotion[p],closest_explotion[x]+1);
continue;
}
furthest_dynamite[p] = max(furthest_dynamite[p],furthest_dynamite[x]+1);
closest_explotion[p] = min(closest_explotion[p],closest_explotion[x]+1);
}
}
}
int main(){
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> m;
for(int i = 1; i <= n; i++){
cin >> is_dynamite[i];
}
for(int i = 1; i < n; i++){
int x,y;
cin >> x >> y;
gr[x].pb(y);
gr[y].pb(x);
}
dfs(1,0);
int l = 0, r = n;
int answer = -1;
while(l <= r){
int mid = l+r;
mid >>= 1;
if(check(mid)){
r = mid-1;
answer = mid;
} else {
l = mid+1;
}
}
cout << answer << endl;
}
Compilation message (stderr)
dyn.cpp: In function 'bool check(int)':
dyn.cpp:58:1: warning: control reaches end of non-void function [-Wreturn-type]
}
^
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