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。

通过前序得到根，利用中序分割左子树右子树，递归解决问题。

class Solution1 {

public:

    struct TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> in) {

        int in_size = in.size();

        if(in_size == 0)

            return NULL;

        vector<int> pre_left, pre_right, in_left, in_right;

        int val = pre[0];

        TreeNode* node = new TreeNode(val);//root node is the first element in pre

        int p = 0;

        for(p; p < in_size; ++p){

            if(in[p] == val) //Find the root position in in

                break;

        }

        for(int i = 0; i < in_size; ++i){

            if(i < p){

                in_left.push_back(in[i]);//Construct the left pre and in

                pre_left.push_back(pre[i+1]);

            }

            else if(i > p){

                in_right.push_back(in[i]);//Construct the right pre and in

                pre_right.push_back(pre[i]);

            }

        }

        node->left = reConstructBinaryTree(pre_left, in_left);

        node->right = reConstructBinaryTree(pre_right, in_right);

        return node;

    }

};