剑指offer
2018-3-13
请实现一个函数按照之字形打印二叉树
1 思路:两个栈
1 import java.util.*; 2 3 /* 4 public class TreeNode { 5 int val = 0; 6 TreeNode left = null; 7 TreeNode right = null; 8 9 public TreeNode(int val) { 10 this.val = val; 11 12 } 13 14 } 15 */ 16 public class Solution { 17 public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) { 18 ArrayList<ArrayList<Integer>> res = new ArrayList<>(); 19 if (pRoot == null) { 20 return res; 21 } 22 Stack<TreeNode> stack1 = new Stack<>(); 23 Stack<TreeNode> stack2 = new Stack<>(); 24 stack1.push(pRoot); 25 while (!stack1.isEmpty() || !stack2.isEmpty()) { 26 ArrayList<Integer> layer = new ArrayList<>(); 27 while (!stack1.isEmpty()) { 28 TreeNode node = stack1.pop(); 29 layer.add(node.val); 30 if (node.left != null) { 31 stack2.push(node.left); 32 } 33 if (node.right != null) { 34 stack2.push(node.right); 35 } 36 } 37 res.add(layer); 38 layer = new ArrayList<>(); 39 while (!stack2.isEmpty()) { 40 TreeNode node = stack2.pop(); 41 layer.add(node.val); 42 if (node.right != null) { 43 stack1.push(node.right); 44 } 45 if (node.left != null) { 46 stack1.push(node.left); 47 } 48 } 49 if (!layer.isEmpty()) { 50 res.add(layer); 51 } 52 } 53 return res; 54 } 55 56 }
把二叉树打印成多行:从上到下按
1 import java.util.ArrayList; 2 3 4 /* 5 public class TreeNode { 6 int val = 0; 7 TreeNode left = null; 8 TreeNode right = null; 9 10 public TreeNode(int val) { 11 this.val = val; 12 13 } 14 15 } 16 */ 17 public class Solution { 18 ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) { 19 20 } 21 22 }
层打印二叉树,同一层结点从左至右输出。每一层输出一行。