我的构建二叉树解决方案有什么问题？

Question

我尝试在其预订和顺序遍历上构建二叉树条件.

但是,当我运行下面的代码时,20%的测试样本通过,然后我得到了"1351分段错误(核心转储)",其中preorder = inorder = {1,2}.

我的代码有什么问题？以及如何在linux上调试"分段故障"？

谢谢!!!

class Solution {
    /**
     *@param preorder : A list of integers that preorder traversal of a tree
     *@param inorder : A list of integers that inorder traversal of a tree
     *@return : Root of a tree
     */
public:
    TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) {
        // write your code here
        TreeNode * root;
        if (preorder.empty() || inorder.empty()) {
            cout<<"in if"<<endl;
            return NULL;
        }
        root->val = preorder.front();  
        vector<int> inorder_left(inorder.begin(), inorder.begin() + getIndex(inorder, preorder.front()));     
        vector<int> inorder_right(inorder.begin() + getIndex(inorder, preorder.front()) + 1, inorder.end());  
        vector<int> preorder_left(preorder.begin() + 1, preorder.begin() + 1 + inorder_left.size()); 
        vector<int> preorder_right(preorder.begin() + 1 + inorder_left.size(), preorder.end());        
        root->left = buildTree(preorder_left, inorder_left);   
        root->right = buildTree(preorder_right, inorder_right);
        return root;
    }
private:
    int getIndex(vector<int> & vec, int target) {
        for (int i = 0; i < vec.size(); i++) {
            if (vec[i] == target) {
                return i;
            }
        }
    }
};

Answer 1

root访问其成员时val,指针未初始化,left并且right.new TreeNode()例如,用它初始化它.