題目描述
輸入某二叉樹的前序遍歷和中序遍歷的結果，請重建出該二叉樹。假設輸入的前序遍歷和中序遍歷的結果中都不含重複的數字。例如輸入前序遍歷序列{1,2,4,7,3,5,6,8}和中序遍歷序列{4,7,2,1,5,3,8,6}，則重建二叉樹並返回。

class Solution {
public:
    TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> vin) {
    int pre_len = pre.size();
    int in_len = vin.size();
    if(pre_len == 0 || in_len == 0 || pre_len != in_len)
        return NULL;
    TreeNode *head = new TreeNode(pre[0]);//建立根節點
    int root_ind = 0;//記錄root在中序中的下標
    for(int i = 0; i<pre_len; i++){
        if(vin[i] == pre[0]){
            root_ind = i;
            break;
        }
    }
    vector<int> in_left, in_right,pre_left, pre_right;
    for(int j = 0; j<root_ind; j++){
        in_left.push_back(vin[j]);
        pre_left.push_back(pre[j+1]);//第一個為根根節點，跳過
    }
    for(int j = root_ind+1; j<pre_len; j++){
        in_right.push_back(vin[j]);
        pre_right.push_back(pre[j]);
    }
    //遞迴
    head->right = reConstructBinaryTree(pre_right, in_right);
    head->left = reConstructBinaryTree(pre_left, in_left);
    return head;
    }
};