根据先序中序遍历建树【模板】

主要就是通过先序找到当前子树根节点，再用中序遍历分子树，不断递归下去。

#include <iostream>#include <stdio.h>#include <cstring>#include <vector>#include <cmath>#include <algorithm>#include <set>#include <cassert>#include <time.h>#include <queue>#include <map>#include <stack>#include <bitset>#include <string>#include <sstream>#define INF 0x3f3f3f3fusing namespace std;template <class Type>Type stringToNum(const string& str){    istringstream iss(str);    Type num;    iss >> num;    return num;    }//======================================================typedef struct node{    int m_key;    node * m_pLeft,*m_pRight;}BinaryTreeNode;//BinaryTreeNode* constructTree(int* preOrder,int preLen,int* sMidOrder, int midLen){BinaryTreeNode* constructRoot(int* preOrder, int* midOrder, int len){    //先根遍历（前序遍历）的第一个值就是根节点的key    int rootKey=preOrder[0];    BinaryTreeNode* root=new BinaryTreeNode;    root->m_key=rootKey;    root->m_pLeft=root->m_pRight=NULL;    if(len==1 && *preOrder==*midOrder)//只有一个节点        return root;    //在中根遍历（中序遍历）中找到根节点    int* rootMidOrder=midOrder;    int leftLen=0; //左子树节点数    while(*rootMidOrder!=rootKey&&rootMidOrder<=(midOrder+len-1)){         ++rootMidOrder;        ++leftLen;    }    if(*rootMidOrder!=rootKey)//在中根序列未找到根节点，输入错误        return NULL;    if(leftLen>0){ //构建左子树        root->m_pLeft=constructRoot(preOrder+1,midOrder,leftLen);    }    if(len-leftLen-1>0){ //构建右子树        root->m_pRight=constructRoot(preOrder+leftLen+1,rootMidOrder+1,len-leftLen-1);    }    return root;}BinaryTreeNode* construct(int* preOrder,int* midOrder,int len){    if(preOrder==NULL||midOrder==NULL||len<=0)        return NULL;    return constructRoot(preOrder,midOrder,len);}//先根遍历void preOrderRecursionPrint(BinaryTreeNode* root){    if(root==NULL)        return;    cout<<root->m_key<<endl;   //visit    preOrderRecursionPrint(root->m_pLeft);    preOrderRecursionPrint(root->m_pRight);}int main(){    //freopen("input.txt","r",stdin);    //先根序列    int preOrder[8]={1,2,4,7,3,5,6,8};    //中根序列    int midOrder[8]={4,7,2,1,5,3,8,6};    BinaryTreeNode * treeRoot = construct(preOrder,midOrder,8);    preOrderRecursionPrint(treeRoot);    return 0;}

输出如下：