https://www.luogu.org/problemnew/show/P3379
1.欧拉序+rmq(st)
1 /*
2 在这里，对于一个数，选择最左边的
3 选择任意一个都可以，[left_index,right_index]，深度都大于等于这个数的深度
4 */
5 #include <cstdio>
6 #include <cstdlib>
7 #include <cmath>
8 #include <cstring>
9 #include <time.h>
10 #include <string>
11 #include <set>
12 #include <map>
13 #include <list>
14 #include <stack>
15 #include <queue>
16 #include <vector>
17 #include <bitset>
18 #include <ext/rope>
19 #include <algorithm>
20 #include <iostream>
21 using namespace std;
22 #define ll long long
23 #define minv 1e-6
24 #define inf 1e9
25 #define pi 3.1415926536
26 #define E 2.7182818284
27 const ll mod=1e9+7;//998244353
28 const int maxn=5e5+10;
29
30 struct node
31 {
32 int d;
33 node *next;
34 }*e[maxn];
35
36 int s=0;
37
38 ///每条边走两遍，n-1条边，走2(n-1)个点
39 int a[maxn<<1],b[maxn<<1],f[maxn<<1][20],lef[maxn],er[20];
40 bool vis[maxn]={0};
41
42 void dfs(int d,int dep)
43 {
44 node* p=e[d];
45 vis[d]=1;
46 s++;
47 lef[d]=s;
48 a[s]=d;
49 b[s]=dep;
50 while (p)
51 {
52 if (!vis[p->d])
53 {
54 dfs(p->d,dep+1);
55 s++;
56 a[s]=d;
57 b[s]=dep;
58 }
59 p=p->next;
60 }
61 }
62
63 int main()
64 {
65 int n,q,root,x,y,i,j,k,m,d;
66 node *p;
67 scanf("%d%d%d",&n,&q,&root);
68 for (i=1;i<n;i++)
69 {
70 scanf("%d%d",&x,&y);
71 p=(node*) malloc (sizeof(node));
72 p->d=y;
73 p->next=e[x];
74 e[x]=p;
75
76 p=(node*) malloc (sizeof(node));
77 p->d=x;
78 p->next=e[y];
79 e[y]=p;
80 }
81 dfs(root,1);
82
83 m=log(s)/log(2);
84 er[0]=1;
85 for (i=1;i<=m;i++)
86 er[i]=er[i-1]<<1;
87 for (i=1;i<=s;i++)
88 f[i][0]=i;
89 // f[i][0]=b[i];
90 for (i=1;i<=m;i++) //2^i
91 for (j=1,k=j+er[i-1];j<=s-er[i]+1;j++,k++) //-er[i]+1
92 if (b[ f[j][i-1] ] < b[ f[k][i-1] ])
93 f[j][i]=f[j][i-1];
94 else
95 f[j][i]=f[k][i-1];
96 // f[j][i]=min(f[j][i-1],f[j+er[i-1]][i-1]);
97
98 while (q--)
99 {
100 scanf("%d%d",&x,&y);
101 x=lef[x];
102 y=lef[y];
103 if (x>y)
104 swap(x,y);
105 d=log(y-x+1)/log(2);
106 j=y-er[d]+1;
107 if (b[ f[x][d] ] < b[ f[j][d] ]) //+1
108 printf("%d\n",a[ f[x][d] ]);
109 else
110 printf("%d\n",a[ f[j][d] ]);
111 // printf("%d\n",min(f[x][d],f[y-er[d]+1][d]));
112 }
113 return 0;
114 }
115 /*
116 8 100 1
117 1 2
118 1 3
119 2 4
120 2 5
121 3 6
122 5 7
123 6 8
124
125 5 7
126 5
127 2 3
128 1
129 3 2
130 1
131 1 8
132 1
133 2 8
134 1
135 4 5
136 2
137 5 4
138 2
139 */
2.欧拉序+线段树
1 /*
2 在这里，对于一个数，选择最左边的
3 选择任意一个都可以，[left_index,right_index]，深度都大于等于这个数的深度
4 */
5 #include <cstdio>
6 #include <cstdlib>
7 #include <cmath>
8 #include <cstring>
9 #include <time.h>
10 #include <string>
11 #include <set>
12 #include <map>
13 #include <list>
14 #include <stack>
15 #include <queue>
16 #include <vector>
17 #include <bitset>
18 #include <ext/rope>
19 #include <algorithm>
20 #include <iostream>
21 using namespace std;
22 #define ll long long
23 #define minv 1e-6
24 #define inf 1e9
25 #define pi 3.1415926536
26 #define E 2.7182818284
27 const ll mod=1e9+7;//998244353
28 const int maxn=5e5+10;
29
30 struct node
31 {
32 int d;
33 node *next;
34 }*e[maxn];
35
36 int s=0;
37
38 ///每条边走两遍，n-1条边，走2(n-1)个点
39 int a[maxn<<1],b[maxn<<1],lef[maxn],f[maxn<<3];
40 bool vis[maxn]={0};
41 int num=0;
42
43 void dfs(int d,int dep)
44 {
45 node* p=e[d];
46 vis[d]=1;
47 s++;
48 lef[d]=s;
49 a[s]=d;
50 b[s]=dep;
51 while (p)
52 {
53 if (!vis[p->d])
54 {
55 dfs(p->d,dep+1);
56 s++;
57 a[s]=d;
58 b[s]=dep;
59 }
60 p=p->next;
61 }
62 }
63
64 void build(int index,int l,int r)
65 {
66 if (l==r)
67 f[index]=++num;
68 else
69 {
70 int m=(l+r)>>1;
71 build(index<<1,l,m);
72 build(index<<1|1,m+1,r);
73 if (b[f[index<<1]]<b[f[index<<1|1]])
74 f[index]=f[index<<1];
75 else
76 f[index]=f[index<<1|1];
77 }
78 }
79
80 int query(int index,int l,int r,int x,int y)
81 {
82 if (x<=l && r<=y)
83 return f[index];
84 if (r<x || l>y)
85 return 0;
86 int m=(l+r)>>1;
87 int p=query(index<<1,l,m,x,y);
88 int q=query(index<<1|1,m+1,r,x,y);
89 if (b[p]<b[q])
90 return p;
91 else
92 return q;
93 }
94
95 int main()
96 {
97 int n,q,root,x,y,i,j,m,d;
98 node *p;
99 scanf("%d%d%d",&n,&q,&root);
100 for (i=1;i<n;i++)
101 {
102 scanf("%d%d",&x,&y);
103 p=(node*) malloc (sizeof(node));
104 p->d=y;
105 p->next=e[x];
106 e[x]=p;
107
108 p=(node*) malloc (sizeof(node));
109 p->d=x;
110 p->next=e[y];
111 e[y]=p;
112 }
113 dfs(root,1);
114
115 b[0]=n+1;
116 build(1,1,s);
117 while (q--)
118 {
119 scanf("%d%d",&x,&y);
120 x=lef[x];
121 y=lef[y];
122 if (x>y)
123 swap(x,y);
124 printf("%d\n",a[query(1,1,s,x,y)]);
125 }
126 return 0;
127 }
3.离线dfs
1 #include <cstdio>
2 #include <cstdlib>
3 #include <cmath>
4 #include <cstring>
5 #include <time.h>
6 #include <string>
7 #include <set>
8 #include <map>
9 #include <list>
10 #include <stack>
11 #include <queue>
12 #include <vector>
13 #include <bitset>
14 #include <ext/rope>
15 #include <algorithm>
16 #include <iostream>
17 using namespace std;
18 #define ll long long
19 #define minv 1e-6
20 #define inf 1e9
21 #define pi 3.1415926536
22 #define E 2.7182818284
23 const ll mod=1e9+7;//998244353
24 const int maxn=5e5+10;
25
26 struct node
27 {
28 int d;
29 node *next;
30 }*e[maxn];
31 struct rec
32 {
33 int d,index;
34 rec *next;
35 }*ask[maxn];
36 bool vis[maxn]={0};
37
38 int r[maxn],fa[maxn];
39
40 int getfather(int d)
41 {
42 if (fa[d]==d)
43 return d;
44 fa[d]=getfather(fa[d]);
45 return fa[d];
46 }
47
48 void merge(int x,int y)
49 {
50 int s=getfather(x);
51 int t=getfather(y);
52 fa[t]=s;
53 }
54
55 void dfs(int d)
56 {
57 node *p;
58 rec *v;
59 vis[d]=1;
60
61 p=e[d];
62 while (p)
63 {
64 if (!vis[p->d])
65 {
66 dfs(p->d);
67 merge(d,p->d);
68 }
69 p=p->next;
70 }
71
72 v=ask[d];
73 while (v)
74 {
75 if (vis[v->d])
76 r[v->index]=getfather(v->d);
77 v=v->next;
78 }
79 }
80
81 int main()
82 {
83 node *p;
84 rec *v;
85 int n,q,root,x,y,i;
86 scanf("%d%d%d",&n,&q,&root);
87 for (i=1;i<n;i++)
88 {
89 scanf("%d%d",&x,&y);
90 p=(node*) malloc (sizeof(node));
91 p->d=y;
92 p->next=e[x];
93 e[x]=p;
94
95 p=(node*) malloc (sizeof(node));
96 p->d=x;
97 p->next=e[y];
98 e[y]=p;
99 }
100
101 for (i=1;i<=q;i++)
102 {
103 scanf("%d%d",&x,&y);
104 v=(rec*) malloc (sizeof(rec));
105 v->d=y;
106 v->index=i;
107 v->next=ask[x];
108 ask[x]=v;
109
110 v=(rec*) malloc (sizeof(rec));
111 v->d=x;
112 v->index=i;
113 v->next=ask[y];
114 ask[y]=v;
115 }
116
117 for (i=1;i<=n;i++)
118 fa[i]=i;
119 dfs(root);
120 for (i=1;i<=q;i++)
121 printf("%d\n",r[i]);
122 return 0;
123 }
原文地址：https://www.cnblogs.com/cmyg/p/9545267.html
时间： 2024-08-04 11:30:55