剑指Offer:重建二叉树

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中都不含重复的数字。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}，则重建二叉树并返回。

struct TreeNode{
  
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x):val(x),left(NULL),right(NULL){}
  
};
  
  
class Solution{
public:
    TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> vin) {
  
        TreeNode* root=reConstructBinaryTreeOne(pre,0,pre.size()-1,vin,0,vin.size()-1);
        return root;
    }
  
    //前序遍历{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}
private:
    TreeNode* reConstructBinaryTreeOne(vector<int> pre,int startPre,int endPre,vector<int> vin,int startIn,int endIn) {
  
        if(startPre>endPre||startIn>endIn)
            return nullptr;
        TreeNode* root=new TreeNode(pre[startPre]);
  
        for(int i=startIn;i<=endIn;i++)
            if(vin[i]==pre[startPre]){
                root->left=reConstructBinaryTreeOne(pre,startPre+1,startPre+i-startIn,vin,startIn,i-1);
                root->right=reConstructBinaryTreeOne(pre,i-startIn+startPre+1,endPre,vin,i+1,endIn);
                break;
            }
  
            return root;
    }
};