面试题6 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 NULL;
        }
        int i;
        vector<int> pre1, pre2, in1, in2;
        for (i = 0; i < in.size(); i++){
            if (pre[0] != in[i]){
                in1.push_back(in[i]);
                pre1.push_back(pre[i + 1]);
            }
            else
                break;
        }
        if (i == in.size())
            return NULL;
        struct TreeNode *root = new TreeNode(pre[0]);

        for (int k = i + 1; k < in.size(); k++){
            in2.push_back(in[k]);
            pre2.push_back(pre[k]);
        }

        root->left = reConstructBinaryTree(pre1, in1);
        root->right = reConstructBinaryTree(pre2, in2);
        return root;
    }
};