重建二叉树

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。

注意C++

• 值传递
• 引用传递
• 指针传递

/**
 * 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> vin) {
        return reConstructBinaryTree(pre, 0, pre.size()-1, vin, 0, vin.size()-1);
    }
    
    TreeNode* reConstructBinaryTree(vector<int>& pre, int i, int j, vector<int>& in, int m, int n) {
        if (i > j || m > n) {
            return NULL;
        }
        TreeNode* root = new TreeNode(pre[i]);
        int k = m;
        for (; k <= n && in[k] != root->val; k++);
        // left tree size k-m
        root->left = reConstructBinaryTree(pre, i+1, i+(k-m), in, m, k-1);
        root->right = reConstructBinaryTree(pre, i+(k-m)+1, j, in, k+1, n);
        return root;
    }
};