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); } }