poj 1330 Nearest Common Ancestors 题解
来源:互联网 发布:java身份证号计算年龄 编辑:程序博客网 时间:2024/05/17 08:21
Nearest Common AncestorsView Code
Time Limit: 1000MS Memory Limit: 10000KTotal Submissions: 24618 Accepted: 12792
Description
A rooted tree is a well-known data structure in computer science and engineering. An example is shown below:
In the figure, each node is labeled with an integer from {1, 2,...,16}. Node 8 is the root of the tree. Node x is an ancestor of node y if node x is in the path between the root and node y. For example, node 4 is an ancestor of node 16. Node 10 is also an ancestor of node 16. As a matter of fact, nodes 8, 4, 10, and 16 are the ancestors of node 16. Remember that a node is an ancestor of itself. Nodes 8, 4, 6, and 7 are the ancestors of node 7. A node x is called a common ancestor of two different nodes y and z if node x is an ancestor of node y and an ancestor of node z. Thus, nodes 8 and 4 are the common ancestors of nodes 16 and 7. A node x is called the nearest common ancestor of nodes y and z if x is a common ancestor of y and z and nearest to y and z among their common ancestors. Hence, the nearest common ancestor of nodes 16 and 7 is node 4. Node 4 is nearer to nodes 16 and 7 than node 8 is.
For other examples, the nearest common ancestor of nodes 2 and 3 is node 10, the nearest common ancestor of nodes 6 and 13 is node 8, and the nearest common ancestor of nodes 4 and 12 is node 4. In the last example, if y is an ancestor of z, then the nearest common ancestor of y and z is y.
Write a program that finds the nearest common ancestor of two distinct nodes in a tree.
In the figure, each node is labeled with an integer from {1, 2,...,16}. Node 8 is the root of the tree. Node x is an ancestor of node y if node x is in the path between the root and node y. For example, node 4 is an ancestor of node 16. Node 10 is also an ancestor of node 16. As a matter of fact, nodes 8, 4, 10, and 16 are the ancestors of node 16. Remember that a node is an ancestor of itself. Nodes 8, 4, 6, and 7 are the ancestors of node 7. A node x is called a common ancestor of two different nodes y and z if node x is an ancestor of node y and an ancestor of node z. Thus, nodes 8 and 4 are the common ancestors of nodes 16 and 7. A node x is called the nearest common ancestor of nodes y and z if x is a common ancestor of y and z and nearest to y and z among their common ancestors. Hence, the nearest common ancestor of nodes 16 and 7 is node 4. Node 4 is nearer to nodes 16 and 7 than node 8 is.
For other examples, the nearest common ancestor of nodes 2 and 3 is node 10, the nearest common ancestor of nodes 6 and 13 is node 8, and the nearest common ancestor of nodes 4 and 12 is node 4. In the last example, if y is an ancestor of z, then the nearest common ancestor of y and z is y.
Write a program that finds the nearest common ancestor of two distinct nodes in a tree.
Input
The input consists of T test cases. The number of test cases (T) is given in the first line of the input file. Each test case starts with a line containing an integer N , the number of nodes in a tree, 2<=N<=10,000. The nodes are labeled with integers 1, 2,..., N. Each of the next N -1 lines contains a pair of integers that represent an edge --the first integer is the parent node of the second integer. Note that a tree with N nodes has exactly N - 1 edges. The last line of each test case contains two distinct integers whose nearest common ancestor is to be computed.
Output
Print exactly one line for each test case. The line should contain the integer that is the nearest common ancestor.
Sample Input
2161 148 510 165 94 68 44 101 136 1510 116 710 216 38 116 1216 752 33 43 11 53 5
Sample Output
43
Source
Taejon 2002
[Submit] [Go Back] [Status] [Discuss]
Home Page Go Back To top
————————————————————我是分割线————————————————————————————————
水题一道,LCA果题。
果断解决。
1 #include<iostream> 2 #include<cstring> 3 #include<cstdio> 4 #include<vector> 5 using namespace std; 6 const int N=10002; 7 const int Log=20; 8 int dp[N][Log],depth[N],deg[N]; 9 struct Edge10 {11 int to;12 Edge *next;13 }edge[2*N],*cur,*head[N];14 void addedge(int u,int v)15 {16 cur->to=v;17 cur->next=head[u];18 head[u]=cur++;19 }20 void dfs(int u)21 {22 depth[u]=depth[dp[u][0]]+1;23 for(int i=1;i<Log;i++) dp[u][i]=dp[dp[u][i-1]][i-1];24 for(Edge *it=head[u];it;it=it->next)25 {26 dfs(it->to);27 }28 }29 int lca(int u,int v)30 {31 if(depth[u]<depth[v])swap(u,v);32 for(int st=1<<(Log-1),i=Log-1;i>=0;i--,st>>=1)33 {34 if(st<=depth[u]-depth[v])35 {36 u=dp[u][i];37 }38 }39 if(u==v) return u;40 for(int i=Log-1;i>=0;i--)41 {42 if(dp[v][i]!=dp[u][i])43 {44 v=dp[v][i];45 u=dp[u][i];46 }47 }48 return dp[u][0];49 }50 void init(int n)51 {52 for(int i=0;i<=n;i++)53 {54 dp[i][0]=0;55 head[i]=NULL;56 deg[i]=0;57 }58 cur=edge;59 }60 int main()61 {62 int T;63 scanf("%d",&T);64 while(T--)65 {66 int n,u,v;67 scanf("%d",&n);68 init(n);69 for(int i=0;i<n-1;i++)70 {71 scanf("%d%d",&u,&v);72 addedge(u,v);73 deg[v]++;74 dp[v][0]=u;75 }76 for(int i=1;i<=n;i++)77 {78 if(deg[i]==0)79 {80 dfs(i);81 break;82 }83 }84 scanf("%d%d",&u,&v);85 printf("%d\n",lca(u,v));86 }87 return 0;88 }
0 0
- POJ 1330 Nearest Common Ancestors LCA题解
- poj 1330 Nearest Common Ancestors 题解
- POJ 1330 Nearest Common Ancestors
- poj 1330 Nearest Common Ancestors
- poj 1330 Nearest Common Ancestors
- POJ 1330 Nearest Common Ancestors
- POJ 1330 Nearest Common Ancestors
- POJ 1330 Nearest Common Ancestors
- poj - 1330 - Nearest Common Ancestors
- poj 1330 Nearest Common Ancestors
- poj 1330 Nearest Common Ancestors
- POJ 1330 Nearest Common Ancestors
- poj 1330 Nearest Common Ancestors
- poj 1330 Nearest Common Ancestors
- poj 1330 Nearest Common Ancestors
- POJ 1330:Nearest Common Ancestors
- POJ 1330 Nearest Common Ancestors
- POJ---1330-Nearest Common Ancestors
- JSP学习笔记
- 学习笔记:快速幂
- tyvj 2075 借教室 题解
- 学习笔记:树分治
- C语言strlen()函数:返回字符串的长度
- poj 1330 Nearest Common Ancestors 题解
- Unknown type name 'NSString'
- Nescafé2 月之谜 题解
- python(2)
- 学习笔记:STL
- gson
- Android动态加载dex技术初探
- C++ 竞赛常用头文件
- 学习笔记:单调队列