【hot100-java】【二叉树的层序遍历】
二叉树
BFS
队列实现
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public List<List<Integer>> levelOrder(TreeNode root) {
Queue<TreeNode> queue=new LinkedList<>();
List<List<Integer>>ret=new ArrayList<>();
if(root!=null) queue.add(root);
while(!queue.isEmpty()){
List<Integer>tmp=new ArrayList<>();
for(int i=queue.size();i>0;i--){
TreeNode node=queue.poll();
tmp.add(node.val);
if(node.left!=null) queue.add(node.left);
if(node.right!=null) queue.add(node.right);
}
ret.add(tmp);
}
return ret;
}
} 