Binary Tree Level Order Traversal

给一个二叉树, 层序扫描. 这个最常见的扫描方法.

/**
 * 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) {
        ArrayList<List<Integer>> res = new ArrayList<List<Integer>>();
        if(root == null)
            return res;
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.offer(root);
        while(!queue.isEmpty()){
            List<Integer> tmp = new ArrayList<Integer>();
            int size = queue.size();
            for(int i = 0 ; i < size; i++) {
                TreeNode node = queue.poll();
                tmp.add(node.val);
                if(node.left != null)
                    queue.offer(node.left);
                if(node.right != null)
                    queue.offer(node.right);
            }
            res.add(tmp);
        }
        return res;
    }
}

/**

* 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) {

ArrayList<List<Integer>> res = new ArrayList<List<Integer>>();

if(root == null)

return res;

Queue<TreeNode> queue = new LinkedList<TreeNode>();

queue.offer(root);

while(!queue.isEmpty()){

List<Integer> tmp = new ArrayList<Integer>();

int size = queue.size();

for(int i = 0 ; i < size; i++) {

TreeNode node = queue.poll();

tmp.add(node.val);

if(node.left != null)

queue.offer(node.left);

if(node.right != null)

queue.offer(node.right);

}

res.add(tmp);

}

return res;

}

Binary Tree Level Order Traversal

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