剑指offer-重建二叉树

Posted 2021-12-14 jawen

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:
    TreeNode* build(vector<int> v1,int s1,int e1,vector<int> v2,int s2,int e2)
    
        if(s1 >= e1 || s2 >= e2)
            return NULL;
        int k;
        for(k = s2;k < e2;k++)
        
            if(v2[k] == v1[s1])
            
                break;
            
        
        TreeNode* root = new TreeNode(v1[s1]);
        root->left = build(v1,s1+1,s1 + k - s2 + 1,v2,s2,k+1);
        root->right = build(v1,s1 + k - s2 + 1,e1,v2,k+1,e2);
        return root;
    
    TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> vin) 
        return build(pre,0,pre.size(),vin,0,vin.size());
    
;