codevs 1503 愚蠢的宠物

Posted 2020-10-06 Alex丶Baker

1503 愚蠢的宠物

 1 #include<iostream>  
 2 #include<algorithm>  
 3 #include<cstring>  
 4 using namespace std;  
 5   
 6 #define maxn 1000000+100  
 7 int father[maxn];  
 8 int a[maxn],b[maxn];  
 9 int main()  
10 {  
11     int n,x,y;  
12     memset(a,0x3f,sizeof(a));  
13     memset(b,0x3f,sizeof(b));  
14     cin>>n;  
15     for(int i=1;i<=n;i++)  
16         father[i]=i;  
17     for(int i=1;i<n;i++)  
18     {  
19         cin>>x>>y;  
20         father[y]=x;  
21     }  
22     cin>>x>>y;  
23     for(int i=0;i<n;i++)  
24     {  
25         a[x]=min(i,a[x]);  
26         x=father[x];  
27         b[y]=min(i,b[y]);  
28         y=father[y];  
29     }  
30     int mn=999999,ans;  
31     for(int i=1;i<=n;i++)  
32     {  
33         if(a[i]+b[i]<mn){  
34             mn=a[i]+b[i];  
35             ans=i;  
36         }  
37     }  
38     cout<<ans;  
39     return 0;  
40 } 

并查集

 

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 #define maxn 1000000
 4 int n,x,y,head[maxn],num;
 5 int deep[maxn],size[maxn],dad[maxn],top[maxn];
 6 
 7 struct Edge{
 8     int v,next;
 9 }edge[maxn];
10 
11 void add(int u,int v)
12 {
13     edge[++num].v=v;
14     edge[num].next=head[u];
15     head[u]=num;
16 }
17 
18 void dfs(int x)
19 {
20     size[x]=1 ; deep[x]=deep[dad[x]]+1;
21     for(int i=head[x];i;i=edge[i].next)
22     {
23         int v=edge[i].v;
24         if(dad[x]==v) continue;
25         dad[v]=x; dfs(v); size[x]+=size[v];
26      }
27 }
28 
29 void dfs2(int x)
30 {
31     int t=0; if(!top[x]) top[x]=x;
32     for(int i=head[x];i;i=edge[i].next)
33     {
34         int v=edge[i].v;
35         if(dad[x]!=v&&size[t]<size[v]) t=v;
36     }
37     if(t) top[t]=top[x],dfs2(t);
38     for(int i=head[x];i;i=edge[i].next)
39     {
40         int v=edge[i].v;
41         if(dad[x]!=v&&t!=v) dfs2(v);
42     }
43 }
44 
45 int lca(int x,int y)
46 {
47     for(;top[x]!=top[y];x=dad[top[x]])
48         if(deep[top[x]]<deep[top[y]]) swap(x,y);
49     return deep[x]<deep[y]?x:y;
50 }
51 
52 
53 int main()
54 {
55     scanf("%d",&n);
56     for(int i=1;i<n;i++)
57     {
58         scanf("%d%d",&x,&y);
59         add(x,y); add(y,x);
60     }
61     dfs(1); dfs2(1);
62     int a,b,ans;
63     scanf("%d%d",&a,&b);
64     printf("%d",lca(a,b));
65     return 0;
66 }

LCA