标签：Binary 结点 int ERROR Tree pos LCA found inRoot

The lowest common ancestor (LCA) of two nodes U and V in a tree is the deepest node that has both U and V as descendants.

Given any two nodes in a binary tree, you are supposed to find their LCA.

Input Specification:

Each input file contains one test case. For each case, the first line gives two positive integers: M (≤ 1,000), the number of pairs of nodes to be tested; and N (≤ 10,000), the number of keys in the binary tree, respectively. In each of the following two lines, N distinct integers are given as the inorder and preorder traversal sequences of the binary tree, respectively. It is guaranteed that the binary tree can be uniquely determined by the input sequences. Then M lines follow, each contains a pair of integer keys U and V. All the keys are in the range of int.

Output Specification:

For each given pair of U and V, print in a line LCA of U and V is A. if the LCA is found and A is the key. But if A is one of U and V, print X is an ancestor of Y. where X is A and Y is the other node. If U or V is not found in the binary tree, print in a line ERROR: U is not found. or ERROR: V is not found. or ERROR: U and V are not found..

Sample Input:

6 8
7 2 3 4 6 5 1 8
5 3 7 2 6 4 8 1
2 6
8 1
7 9
12 -3
0 8
99 99

Sample Output:

LCA of 2 and 6 is 3.
8 is an ancestor of 1.
ERROR: 9 is not found.
ERROR: 12 and -3 are not found.
ERROR: 0 is not found.
ERROR: 99 and 99 are not found.

生词

题目大意：

给出中序序列和先序序列，再给出两个点，求这两个点的最近公共祖先～

分析：

不用建树～已知某个树的根结点，若a和b在根结点的左边，则a和b的最近公共祖先在当前子树根结点的左子树寻找，如果a和b在当前子树根结点的两边，在当前子树的根结点就是a和b的最近公共祖先，如果a和b在当前子树根结点的右边，则a和b的最近公共祖先就在当前子树的右子树寻找。中序加先序可以唯一确定一棵树，在不构建树的情况下，在每一层的递归中，可以得到树的根结点，在此时并入lca算法可以确定两个结点的公共祖先～

原文链接：https://blog.csdn.net/liuchuo/article/details/82560863

题解

#include <bits/stdc++.h>

using namespace std;
map<int,int> pos;
vector<int> in,pre;
void lca(int inl,int inr,int preRoot,int a,int b)
{
    if(inl>inr) return;
    int inRoot=pos[pre[preRoot]],aIn=pos[a],bIn=pos[b];
    if(aIn<inRoot&&bIn<inRoot)
        lca(inl,inRoot-1,preRoot+1,a,b);
    else if((aIn<inRoot&&bIn>inRoot)||(aIn>inRoot&&bIn<inRoot))
        printf("LCA of %d and %d is %d.\n", a, b, in[inRoot]);
    else if(aIn>inRoot&&bIn>inRoot)
        lca(inRoot+1,inr,preRoot+1+(inRoot-inl),a,b);
    else if(aIn==inRoot)
        printf("%d is an ancestor of %d.\n", a, b);
    else if(bIn==inRoot)
        printf("%d is an ancestor of %d.\n", b, a);

}
int main()
{
    #ifdef ONLINE_JUDGE
#else
    freopen("1.txt", "r", stdin);
#endif
    int m,n,a,b;
    cin>>m>>n;
    in.resize(n+1);pre.resize(n+1);
    for(int i=1;i<=n;i++){
        cin>>in[i];
        pos[in[i]]=i;
    }
    for(int i=1;i<=n;i++) cin>>pre[i];
    for(int i=0;i<m;i++){
        cin>>a>>b;
        if(pos[a]==0&&pos[b]==0)
            printf("ERROR: %d and %d are not found.\n", a, b);
        else if(pos[a]==0||pos[b]==0)
            printf("ERROR: %d is not found.\n", pos[a] == 0 ? a : b);
        else
            lca(1,n,1,a,b);
    }
    return 0;
}

标签：Binary,结点,int,ERROR,Tree,pos,LCA,found,inRoot
来源： https://www.cnblogs.com/moonlight1999/p/15938662.html

本站声明： 1. iCode9 技术分享网（下文简称本站）提供的所有内容，仅供技术学习、探讨和分享；
2. 关于本站的所有留言、评论、转载及引用，纯属内容发起人的个人观点，与本站观点和立场无关；
3. 关于本站的所有言论和文字，纯属内容发起人的个人观点，与本站观点和立场无关；
4. 本站文章均是网友提供，不完全保证技术分享内容的完整性、准确性、时效性、风险性和版权归属；如您发现该文章侵犯了您的权益，可联系我们第一时间进行删除；
5. 本站为非盈利性的个人网站，所有内容不会用来进行牟利，也不会利用任何形式的广告来间接获益，纯粹是为了广大技术爱好者提供技术内容和技术思想的分享性交流网站。