[Algorithm/java] BinaryTree_Level_Order

Problem

Code

package stack_queue;

import java.util.*;

class TreeNode{
    int val;
    TreeNode left, right;
    TreeNode(int x){
        this.val = x;
    }
}

public class BinaryTree_Level_Order {
    
    //Queue
    public static void main(String[] args){
        TreeNode root = new TreeNode(3);
        root.left = new TreeNode(4);
        root.right = new TreeNode(5);
        root.left.left = new TreeNode(6);
        root.left.right = new TreeNode(7);
        System.out.println(solve(root));
    }
    
    public static List<List<Integer>> solve(TreeNode root){
        List<List<Integer>> result = new ArrayList();
        if(root==null){
            return result;
        }
        
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        
        //2 
        while(!queue.isEmpty()){
            int size = queue.size();
            List<Integer> list = new LinkedList<>();
            for(int i=0; i<size; i++){
                TreeNode node = queue.poll(); //값을 뺀다.
                list.add(node.val);
                if(node.left != null){
                    queue.offer(node.left);
                }
                if(node.right != null){
                    queue.offer(node.right);
                }
            }
            result.add(list);
        }
        
        return result;
    }
    
    
}

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