【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。

 

/**
 * 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* reConstructBinaryTree(vector<int> pre,vector<int> in)
    {
        int len = pre.size();
        if(len <= 0) return NULL;
        int index;
        for(int i=0; i<len; i++) {
            if(in[i] == pre[0]) {
                index = i;
                break;
            }
        }
        vector<int>lpre, rpre, lin, rin;
        for(int i=0; i<index; i++) {
            lpre.push_back(pre[i+1]);
            lin.push_back(in[i]);
        }
        for(int i=index+1; i<len; i++) {
            rpre.push_back(pre[i]);
            rin.push_back(in[i]);
        }
        TreeNode* T = (TreeNode*)malloc(sizeof(TreeNode));
        T->val = pre[0];
        T->left = reConstructBinaryTree(lpre, lin);
        T->right = reConstructBinaryTree(rpre, rin);
        return T;
    }
};