IT工程師數位筆記本

從上到下按層打印二叉樹，同一層結點從左至右輸出。每一層輸出一行。

import java.util.ArrayList;
import java.util.LinkedList;

 class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
public class Solution {
    ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {

        ArrayList<ArrayList<Integer>> level = new ArrayList<>();
        ArrayList<Integer> arrays = new ArrayList<>();
        LinkedList<TreeNode> queue = new LinkedList<>();
        if (pRoot == null) {
            return level;
        }
        queue.add(pRoot);
        TreeNode current = null;
        TreeNode last = pRoot;//正在打印的當前行的最右節點
        TreeNode nlast = null;//表示下一行的最右節點
        while (queue.size() != 0) {
            current = queue.poll();
            arrays.add(current.val);
            if (current.left != null) {
                queue.add(current.left);
                nlast = current.left;
            }
            if (current.right != null) {
                queue.add(current.right);
                nlast = current.right;
            }
            if (current == last) {
                level.add(arrays);
                arrays = new ArrayList<>();
                last = nlast;
            }

        }
        return level;

    }

}