剑指Offer-60

题目

从上到下按层打印二叉树，同一层的结点按从左到右的顺序打印，每一层打印一行。

实现

public class Solution60 {
    public static void printTree(BinaryTreeNode root) {
        if (root == null) {
            return;
        }

        Queue<BinaryTreeNode> queue = new ArrayDeque<>();
        BinaryTreeNode node;
        // 当前层的结点个数
        int current = 1;
        // 记录下一层的结点个数
        int next = 0;
        queue.add(root);
        while (!queue.isEmpty()) {
            node = queue.poll();
            current--;
            System.out.printf("%-3d", node.value);

            if (node.left != null) {
                queue.add(node.left);
                next++;
            }
            if (node.right != null) {
                queue.add(node.right);
                next++;
            }

            if (current ==0) {
                System.out.println();
                current = next;
                next = 0;
            }
        }
    }

    public static void main(String[] args) {
        BinaryTreeNode n1 = new BinaryTreeNode(1);
        BinaryTreeNode n2 = new BinaryTreeNode(2);
        BinaryTreeNode n3 = new BinaryTreeNode(3);
        BinaryTreeNode n4 = new BinaryTreeNode(4);
        BinaryTreeNode n5 = new BinaryTreeNode(5);
        BinaryTreeNode n6 = new BinaryTreeNode(6);
        BinaryTreeNode n7 = new BinaryTreeNode(7);
        BinaryTreeNode n8 = new BinaryTreeNode(8);
        BinaryTreeNode n9 = new BinaryTreeNode(9);

        n1.left = n2;
        n1.right = n3;
        n2.left = n4;
        n2.right = n5;
        n3.left = n6;
        n3.right = n7;
        n4.left = n8;
        n4.right = n9;

        printTree(n1);

    }
}