CODEWITHSUNDEEP
javainheritancearraylist
DivyaJyoti Rajdev
DivyaJyoti Rajdev

Reputation: 764

no suitable method found for addAll(List<Integer>)

The following is my code for LeetCode binary tree level order traversal question. It gives a compile error on line 24, for no suitable method found for addAll(List), so I understand thats because addAll(Collections c) is not defined for abstract types i.e. list, but when I change the declaration of thisLevel to ArrayList, I still get the same error.

Why and how should the following be modified to make it a valid assignment?

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> result=new ArrayList<List<Integer>>();
        if(root==null) return result;
        LinkedList<TreeNode> parents=new LinkedList<TreeNode>();
        List<TreeNode> children=new LinkedList<TreeNode>();
        parents.add(root);
        List<Integer> thisLevel=new ArrayList<Integer>();
        while(parents.size()!=0 || children.size()!=0){
            TreeNode p=parents.remove();
            thisLevel.add(p.val);
            if(p.left!=null) children.add(p.left);
            if(p.right!=null) children.add(p.right);
            if(parents.size()==0) {
                result.addAll(thisLevel);
                thisLevel=new ArrayList<Integer>();
                parents=children;
                children= new LinkedList<TreeNode>();
            }
        }
        return result;
    }
}

LeetCode Question URL

Upvotes: 1

Views: 4595

Answers (1)

JB Nizet
JB Nizet

Reputation: 691973

The problem is that you're trying to add all the elements of a List<Integer> to a List<List<Integer>>. Since an Integer is not a List<Integer>, that doesn't compile.

Upvotes: 4

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