1151 LCA in a Binary Tree（30 分）

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此题还是比较简单的，根据中序后续建立二叉树，然后DFS查找节点即可

#include<iostream>
#include<cstdio>
#include<set>
using namespace std;

#define MAXN 10005
#define INF 0x7fffffff
#define _for(i,lo,hi) for(int i=(lo);i<(hi);i++)
int preorder[MAXN],inorder[MAXN];
int N,M,K;
struct node{
    int val,height;
    node *lc,*rc,*p;
    node(int v):val(v),height(0),lc(NULL),rc(NULL),p(NULL){}
}; 
node* root;
node* buildTree(int prelo,int prehi,int inlo,int inhi,int h){
    if(prelo>=prehi)return NULL;
    int tmp=preorder[prelo];
    //cout<<tmp<<endl;
    node* cur=new node(tmp);
    cur->height=h;
    int rank=inlo;
    while(inorder[rank]!=tmp){
        rank++;
    }
    cur->lc=buildTree(prelo+1,prelo+1+rank-inlo,inlo,rank,h+1);
    cur->rc=buildTree(prehi-(inhi-rank-1),prehi,rank+1,inhi,h+1);
    if(cur->lc)cur->lc->p=cur;
    if(cur->rc)cur->rc->p=cur;
    return cur;
}
set<int> sset;

node* findnode(int x,node* cur){
    if(!cur)return NULL;
    if(x==cur->val)return cur;
    node* t1=findnode(x,cur->lc); 
    if(t1)return t1;
    node* t2=findnode(x,cur->rc); 
    if(t2)return t2;

    return NULL;
}
int main(){
    //freopen("d:\\input.txt","r",stdin);
    cin>>M>>N;
    _for(i,0,N){cin>>inorder[i];sset.insert(inorder[i]);}
    _for(i,0,N)cin>>preorder[i];
    root=buildTree(0,N,0,N,0);
    if(root->lc)root->lc->p=root;
    if(root->rc)root->rc->p=root;
    int c1,c2;
    _for(i,0,M){
        cin>>c1>>c2;
        bool flag1=true,flag2=true;
        if(sset.count(c1)==0)flag1=false;
        if(sset.count(c2)==0)flag2=false;
        if(flag1&&flag2){
            node* t1=findnode(c1,root);
            node* t2=findnode(c2,root);
            while(t1->height>t2->height)t1=t1->p;
            if(t1->val==t2->val){
                printf("%d is an ancestor of %d.\n",c2,c1);
                continue;
            }
            while(t1->height<t2->height)t2=t2->p;
            if(t1->val==t2->val){
                printf("%d is an ancestor of %d.\n",c1,c2);
                continue;
            }
            while(t1->val!=t2->val){
                t1=t1->p;t2=t2->p;
            }
            printf("LCA of %d and %d is %d.\n",c1,c2,t1->val);
        }else if(flag1){
            printf("ERROR: %d is not found.\n",c2);
        }else if(flag2){
            printf("ERROR: %d is not found.\n",c1);
        }else{
            printf("ERROR: %d and %d are not found.\n",c1,c2);
        }
    }
    return 0;
}