【题目】请实现一个函数按照之字形打印二叉树，
* 即第一行按照从左到右的顺序打印，第二层按照从右至左的顺序打印，第三行按照从左到右的顺序打印，
* 其他行以此类推。
未优化，不是最优解，博主用的是队列，我用的栈。
方法一：直接打印
1 package com.exe7.offer; 2 3 import java.util.Stack; 4 5 import org.junit.Test; 6 7 8 9 /**方法一：直接打印 10 * 【题目】请实现一个函数按照之字形打印二叉树， 11 * 即第一行按照从左到右的顺序打印，第二层按照从右至左的顺序打印，第三行按照从左到右的顺序打印， 12 * 其他行以此类推。 13 * @author WGS 14 * 15 */ 16 public class PrintBiTree { 17 static class TreeNode{ 18 int val=0; 19 TreeNode left=null; 20 TreeNode right=null; 21 public TreeNode(int val){ 22 this.val=val; 23 } 24 } 25 26 27 public void printZhiTree(TreeNode pRoot){ 28 if(pRoot==null) return; 29 Stack<TreeNode> stack1=new Stack<>(); 30 Stack<TreeNode> stack2=new Stack<>(); 31 stack1.push(pRoot); 32 int toBePrint=1; 33 int nextLevelNodes=0; 34 int level=1; 35 TreeNode tempNode=null; 36 37 while(!stack1.isEmpty() || !stack2.isEmpty()){ 38 if(level%2!=0){ 39 tempNode=stack1.pop(); 40 System.out.print(tempNode.val+" "); 41 --toBePrint; 42 if(tempNode.left!=null){ 43 stack2.push(tempNode.left); 44 ++nextLevelNodes; 45 } 46 if(tempNode.right!=null){ 47 stack2.push(tempNode.right); 48 ++nextLevelNodes; 49 } 50 }else{ 51 tempNode=stack2.pop(); 52 System.out.print(tempNode.val+" "); 53 --toBePrint; 54 55 if(tempNode.right!=null){ 56 stack1.push(tempNode.right); 57 ++nextLevelNodes; 58 } 59 if(tempNode.left!=null){ 60 stack1.push(tempNode.left); 61 ++nextLevelNodes; 62 } 63 } 64 // 65 if(toBePrint==0){ 66 System.out.println("------------------"); 67 level++; 68 toBePrint=nextLevelNodes; 69 nextLevelNodes=0; 70 } 71 } 72 73 74 } 75 76 //测试类 77 public static void main(String[] args){ 78 PrintBiTree p=new PrintBiTree(); 79 TreeNode root = new TreeNode(8); 80 TreeNode node1 = new TreeNode(6); 81 TreeNode node2 = new TreeNode(10); 82 TreeNode node3 = new TreeNode(5); 83 TreeNode node4 = new TreeNode(7); 84 TreeNode node5 = new TreeNode(9); 85 TreeNode node6 = new TreeNode(11); 86 TreeNode node7 = new TreeNode(12); 87 TreeNode node8 = new TreeNode(13); 88 TreeNode node9 = new TreeNode(14); 89 TreeNode node10 = new TreeNode(15); 90 TreeNode node11 = new TreeNode(16); 91 TreeNode node12 = new TreeNode(17); 92 TreeNode node13 = new TreeNode(18); 93 TreeNode node14 = new TreeNode(19); 94 95 root.left = node1; 96 root.right = node2; 97 node1.left = node3; 98 node1.right = node4; 99 node2.left = node5; 100 node2.right = node6; 101 node3.left=node7; 102 node3.right=node8; 103 node4.left=node9; 104 node4.right=node10; 105 node5.left=node11; 106 node5.right=node12; 107 node6.left=node13; 108 node6.right=node14; 109 110 111 p.printZhiTree(root); 112 } 113 114 115 116 117 118 }
方法二：面试需要
1 package com.exe7.offer; 2 3 import java.util.ArrayList; 4 import java.util.Stack; 5 6 7 8 9 /**方法二：面试时候需要 10 * 【题目】请实现一个函数按照之字形打印二叉树， 11 * 即第一行按照从左到右的顺序打印，第二层按照从右至左的顺序打印，第三行按照从左到右的顺序打印， 12 * 其他行以此类推。 13 * @author WGS 14 * 15 */ 16 public class PrintBiTree2 { 17 static class TreeNode{ 18 int val=0; 19 TreeNode left=null; 20 TreeNode right=null; 21 public TreeNode(int val){ 22 this.val=val; 23 } 24 } 25 26 27 public ArrayList<ArrayList<Integer>> printZhiTree(TreeNode pRoot){ 28 ArrayList<ArrayList<Integer>> list=new ArrayList<>(); 29 if(pRoot==null) return list; 30 ArrayList<Integer> nodeList=new ArrayList<Integer>(); 31 Stack<TreeNode> stack1=new Stack<>(); 32 Stack<TreeNode> stack2=new Stack<>(); 33 stack1.push(pRoot); 34 int toBePrint=1; 35 int nextLevelNodes=0; 36 int level=1; 37 TreeNode tempNode=null; 38 39 while(!stack1.isEmpty() || !stack2.isEmpty()){ 40 if(level%2!=0){//奇数层 41 tempNode=stack1.pop(); 42 //System.out.print(tempNode.val+" "); 43 nodeList.add(tempNode.val); 44 --toBePrint; 45 if(tempNode.left!=null){ 46 stack2.push(tempNode.left); 47 ++nextLevelNodes; 48 } 49 if(tempNode.right!=null){ 50 stack2.push(tempNode.right); 51 ++nextLevelNodes; 52 } 53 54 }else{ 55 tempNode=stack2.pop(); 56 //System.out.print(tempNode.val+" "); 57 nodeList.add(tempNode.val); 58 --toBePrint; 59 60 if(tempNode.right!=null){ 61 stack1.push(tempNode.right); 62 ++nextLevelNodes; 63 } 64 if(tempNode.left!=null){ 65 stack1.push(tempNode.left); 66 ++nextLevelNodes; 67 } 68 /* if(toBePrint==0){ 69 System.out.println(); 70 list.add(nodeList); 71 level++; 72 toBePrint=nextLevelNodes; 73 nextLevelNodes=0; 74 nodeList=new ArrayList<Integer>(); 75 }*/ 76 } 77 if(toBePrint==0){ 78 System.out.println(); 79 list.add(nodeList); 80 level++; 81 toBePrint=nextLevelNodes; 82 nextLevelNodes=0; 83 nodeList=new ArrayList<Integer>(); 84 } 85 } 86 return list; 87 88 89 } 90 91 //测试类 92 public static void main(String[] args){ 93 PrintBiTree2 p=new PrintBiTree2(); 94 TreeNode root = new TreeNode(8); 95 TreeNode node1 = new TreeNode(6); 96 TreeNode node2 = new TreeNode(10); 97 TreeNode node3 = new TreeNode(5); 98 TreeNode node4 = new TreeNode(7); 99 TreeNode node5 = new TreeNode(9); 100 TreeNode node6 = new TreeNode(11); 101 TreeNode node7 = new TreeNode(12); 102 TreeNode node8 = new TreeNode(13); 103 TreeNode node9 = new TreeNode(14); 104 TreeNode node10 = new TreeNode(15); 105 TreeNode node11 = new TreeNode(16); 106 TreeNode node12 = new TreeNode(17); 107 TreeNode node13 = new TreeNode(18); 108 TreeNode node14 = new TreeNode(19); 109 110 root.left = node1; 111 root.right = node2; 112 node1.left = node3; 113 node1.right = node4; 114 node2.left = node5; 115 node2.right = node6; 116 node3.left=node7; 117 node3.right=node8; 118 node4.left=node9; 119 node4.right=node10; 120 node5.left=node11; 121 node5.right=node12; 122 node6.left=node13; 123 node6.right=node14; 124 125 ArrayList<ArrayList<Integer>> getList=p.printZhiTree(root);; 126 for(ArrayList<Integer> a:getList){ 127 System.out.println(a); 128 } 129 130 } 131 132 133 134 135 136 }