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。

 

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    struct TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> in) {
        if (pre.size() != 0 && in.size() != 0 && pre.size() == in.size())
            {
                return build(pre,in,0,pre.size()-1,0,in.size()-1);
            }
        else
            {
                return NULL;
            }
        
    }
    
    struct TreeNode* build(vector<int> pre,vector<int> in,int l1,int r1,int l2,int r2)
    {
    if(l1<=r1)
    {
        int i=l2;
        while(pre[l1]!=in[i])
            i++;
        TreeNode* T= new TreeNode(in[i]);
        T->left=build(pre,in,l1+1,l1+i-l2,l2,i-1);
        T->right=build(pre,in,l1+i-l2+1,r1,i+1,r2);
        return T;
    }
    else return NULL;
    }
};