从小白开始刷算法 bfs篇 leetcode.107

// 仅是我的思路代码，leetcode上大神更厉害
class Solution {
    public List<List<Integer>> levelOrderBottom(TreeNode root) {
        Queue<TreeNode> q = new LinkedList<>();
        q.add(root);
        LinkedList<List<Integer>> result = new LinkedList<List<Integer>>();
        if(root==null){
            return result;
        }
        while (!q.isEmpty()){
            LinkedList<Integer> list = new LinkedList<>();
            int size = q.size();
            while (size>0){
                TreeNode current = q.poll();
                list.add(current.val);
                if(current.left!=null){
                    q.add(current.left);
                }
                if(current.right!=null){
                    q.add(current.right);
                }
                size--;
            }
            //在link头插进去
            result.addFirst(new LinkedList<>(list));
        }
        return result;
    }
}