runtime error: Reference binding to null pointer of type vector

Question

while I was solving leetcode problem, I was getting reference error. Don't know why??

Here I don't know dimension of vector. If i give some random size to the vector then this code is not giving any error. Is there any other way of doing it??

Line 1034: Char 9: runtime error: reference binding to null pointer of type 'std::vector<int, std::allocator>' (stl_vector.h) SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_vector.h:1043:9

class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* node) {
        vector<vector<int>> ans(4,vector<int>(4));
        queue<TreeNode *> q;
        q.push(node);
        q.push(NULL);
        int row = 0;
        int col = 0;
        while(q.empty() == false){
            TreeNode * temp = q.front();
            if(temp == NULL){

                if(q.size() > 1){
                    q.push(temp);
                    row++;
                    col = 0;
                }

            }
            else{
                ans[row][col] = node->val;
                if(temp->left != NULL){
                    q.push(temp->left);
                }
                if(temp->right != NULL){
                    q.push(temp->right);
                }
            }
            q.pop();
        }
        return ans;
    }
};

Sheikh Parvez Ahmed · Accepted Answer · 2021-11-02 05:36:17Z

-1

Try this code instead, this will work.

class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        vector<vector<int>> ans;
        if(root== NULL) return ans;
        
        queue<TreeNode*> q;
        q.push(root);
        
        while(!q.empty()){
            int size= q.size();
            vector<int> level;
            for(int i=0; i<size; i++){   
                TreeNode* node= q.front();
                q.pop();
                
                level.push_back(node->val);
                
                if(node->left != nullptr) q.push(node->left);
                if(node->right != nullptr) q.push(node->right);   
            }
            ans.push_back(level);
        }
        
        return ans;
        
    }
};

answered Nov 2, 2021 at 5:36

Sheikh Parvez Ahmed

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2 Comments

Nathan Pierson Over a year ago

Could you please add some explanation of where this code differs from the asker's original code and why the change addresses their problem?

Community Over a year ago

As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.

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