Submission #505087

#	Time	Username	Problem	Language	Result	Execution time	Memory
505087		tgbegimx	Untitled (POI11_dyn)	C++17	100 / 100	900 ms	20612 KiB

Main

#include <iostream>
#include <cstdio>
#include <cstring>
#define INF 1000000000
#define maxn 300005
using namespace std;
int n,m;
int a[maxn];
int ans;
struct edge
{
int to,ne;
}b[maxn*2];
int k=0,head[maxn];
int f[maxn],g[maxn];
int limit;
int num=0,op1=0;
inline int read()
{
int x=0,f=1;
char ch=getchar();
while(ch<'0'||ch>'9'){ if(ch=='-') f=-1; ch=getchar(); }
while(ch>='0'&&ch<='9'){ x=x*10+ch-'0'; ch=getchar(); }
return x*f;
}
void add(int u,int v)
{
k++;
b[k].to=v; b[k].ne=head[u]; head[u]=k;
}
void dfs(int x,int pre)
{
f[x]=INF; //The closest distance from the detonated point in the subtree rooted at i to i
if(a[x])
g[x]=0; //The farthest distance between the unexploded point in the subtree rooted at i and i
else
g[x]=-INF;
for(int i=head[x];i!=-1;i=b[i].ne)
if(b[i].to!=pre)
{
dfs(b[i].to,x);
f[x]=min(f[x],f[b[i].to]+1);//Find a tipping point closest to x
g[x]=max(g[x],g[b[i].to]+1);//An unexploded point farthest from x
}
if(g[x]+f[x]<=limit)
//For the subtree rooted at x, there is a tipping point that can detonate those unintended points within a specified time
g[x]=-INF;
if(g[x]==limit)
//The distance from the point farthest from x that failed to be detonated from x = limit, indicating that point x must be ignited
{
f[x]=0,g[x]=-INF,num++;
}
}
bool check(int x)
{
if(!x) return op1<=m;
limit=x; num=0;
dfs(1,0);
if(g[1]+f[1]>limit)
num++;
return num<=m;
}
void getans()
{
int l=0,r=n,mid;
ans=n;
while(l<=r)
{
mid=(l+r)>>1;
if(check(mid)) ans=mid,r=mid-1;
else l=mid+1;
}
}
int main()
{
memset(head,-1,sizeof(head));
n=read(); m=read();
for(int i=1;i<=n;i++)
{
a[i]=read();
if(a[i]) op1++;
}
int x,y;
for(int i=1;i<n;i++)
{
x=read(); y=read();
add(x,y); add(y,x);
}
getans();
printf("%d\n",ans);
return 0;
}

• Subtask 1: 10 / 10
• Subtask 2: 10 / 10
• Subtask 3: 10 / 10
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 10 / 10
• Subtask 9: 10 / 10
• Subtask 10: 10 / 10