剑指Offer系列---(8)重建二叉树

1.题目描述：
输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。假设输入的前序遍历和中序遍历的结果都不含重复的数字。例如输入前序遍历序列{1，2，4，7，3，5，6，8}和中序遍历序列{4，7，2，1，5，3，8，6}，则重建出二叉树并输出它的头结点。二叉树结点的定义如下：
struct BinaryTreeNode
{
    int               m_nValue;
    BinaryTreeNode*   m_pLeft;
    BinaryTreeNode*   m_pRight;

};

2.源代码：

//  Copyright (c) 2015年 skewrain. All rights reserved.

#include <iostream>
#include <stdio.h>
using namespace std;

struct BinaryTreeNode
{
    int               m_nValue;
    BinaryTreeNode*   m_pLeft;
    BinaryTreeNode*   m_pRight;
};

BinaryTreeNode* Construct(int* preorder,int* inorder,int length);

int main(int argc,char *argv[]){
    
    int pre[8] = {1,2,4,7,3,5,6,8};
    int in[8] = {4,7,2,1,5,3,8,6};
    
    BinaryTreeNode *root = Construct(pre, in, 8);
    
    printf("根结点的值为:%d\n",root->m_nValue);

    return 0;
}


BinaryTreeNode* ConstructCore(int* startPreorder,int*endPreorder,int*startInorder,int*endInorder){
    int rootValue = startPreorder[0];
    BinaryTreeNode* root = new BinaryTreeNode();
    root->m_nValue = rootValue;
    root->m_pLeft = root->m_pRight = NULL;
    
    if (startPreorder == endPreorder) {
        if (startInorder == endInorder && *startPreorder == *startInorder)
            return root;
        else
            throw std::exception();
    }
    
    //在中序遍历中找到根节点的值
    int* rootInorder = startInorder;
    while (rootInorder <= endInorder && *rootInorder != rootValue) {
        ++rootInorder;
    }
    
    if(rootInorder == endInorder && *rootInorder != rootValue)
        throw std::exception();
    
    int leftLength = (int)(rootInorder - startInorder);
    int* leftPreorderEnd = startPreorder + leftLength;
    if(leftLength > 0)
    {
        //构建左子树
        root->m_pLeft = ConstructCore(startPreorder+1, leftPreorderEnd, startInorder, rootInorder-1);
    }
    if(leftLength < endPreorder - startPreorder)
    {
        //构建右子树
        root->m_pRight = ConstructCore(leftPreorderEnd+1, endPreorder, rootInorder+1, endInorder);
    }
    return root;
}


BinaryTreeNode *Construct(int* preorder,int* inorder,int length){
    
    if(preorder == NULL || inorder == NULL || length <=0)
        return NULL;
    
    return ConstructCore(preorder, preorder+length-1, inorder, inorder+length-1);
}