# 剑指offer五十九之按之字形顺序打印二叉树

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。

详见代码

```import java.util.ArrayList;
import java.util.Stack;

public class Solution {
public  ArrayList<ArrayList<Integer>> print(TreeNode pRoot) {
int layer = 1;
//s1存奇数层节点
Stack<TreeNode> s1 = new Stack<>();
s1.push(pRoot);
//s2存偶数层节点
Stack<TreeNode> s2 = new Stack<>();

//返回结果
ArrayList<ArrayList<Integer>> list = new ArrayList<>();

while (!s1.empty() || !s2.empty()) {
if (layer % 2 != 0) {
ArrayList<Integer> temp = new ArrayList<>();
while (!s1.empty()) {
TreeNode node = s1.pop();
if (node != null) {
System.out.print(node.val + " ");
s2.push(node.left);
s2.push(node.right);
}
}
if (!temp.isEmpty()) {
layer++;
System.out.println();
}
} else {
ArrayList<Integer> temp = new ArrayList<>();
while (!s2.empty()) {
TreeNode node = s2.pop();
if (node != null) {
System.out.print(node.val + " ");
s1.push(node.right);
s1.push(node.left);
}
}
if (!temp.isEmpty()) {
layer++;
System.out.println();
}
}
}
return list;
}
}```

View Code

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

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

public TreeNode(int val, TreeNode left, TreeNode right) {
this.val = val;
this.left = left;
this.right = right;
}
}```

View Code

```import java.util.ArrayList;

public class TestMain {
public static void main(String[] args) {
//注意必须逆序建立，先建立子节点，再逆序往上建立，因为非叶子结点会使用到下面的节点，而初始化是按顺序初始化的，不逆序建立会报错
TreeNode G = new TreeNode(1, null, null);
TreeNode F = new TreeNode(2, null, null);
TreeNode E = new TreeNode(3, null, null);
TreeNode D = new TreeNode(4, null, null);
TreeNode C = new TreeNode(5, F, G);
TreeNode B = new TreeNode(6, D, E);
TreeNode A = new TreeNode(8, B, C);

ArrayList<ArrayList<Integer>>  arrayList=new ArrayList<>();

Solution s=new Solution();
arrayList= s.print(A);

//之字形遍历输出
for(int i=0;i<arrayList.size();i++){
for (int j=0;j<arrayList.get(i).size();j++){
System.out.print(arrayList.get(i).get(j)+",");
}
System.out.println();
}

}
}```

View Code

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https://www.nowcoder.com/questionTerminal/91b69814117f4e8097390d107d2efbe0

原文作者：hezhiyao
原文地址: https://www.cnblogs.com/hezhiyao/p/7709490.html
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