字节初面

Author: JavaScalaDeveloper

notes/zijie/二叉树蛇形遍历/二叉树蛇形遍历.md

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+标题 二叉树的蛇形遍历
+<p>
+题目描述
+<p>
+实现一个方法，输入二叉树的根节点，实现二叉树的蛇形遍历打印。​
+<p>
+<p>
+<p>
+
+```java
+public class TreeNode {
+    int val;
+    TreeNode left;
+    TreeNode right;
+
+    TreeNode(int x) {
+        val = x;
+    }
+}
+```
+
+<p>
+<p>
+例子：​
+输出 10  5 15 20 12 6 1
+```
+         10
+      5        15
+1      6    12   20
+```
+解法：
+
+```java
+import java.util.*;
+
+public class Main1 {
+    public static void main(String[] args) {
+        TreeNode treeNode = new TreeNode(10, new TreeNode(5, new TreeNode(1, null, null), new TreeNode(6, null, null)),
+                new TreeNode(15, new TreeNode(12, null, null), new TreeNode(20, null, null)));
+        solve(treeNode);
+    }
+
+    private static void solve(TreeNode treeNode) {
+        boolean flag = false;
+        Queue<TreeNode> queue = new LinkedList<>();
+        queue.add(treeNode);
+        while (!queue.isEmpty()) {
+            int size = queue.size();
+            Deque<Integer> list = new LinkedList<>();
+            for (int i = 0; i < size; i++) {
+                TreeNode tree = queue.poll();
+                assert tree != null;
+                int val = tree.val;
+                if (flag) {
+                    list.addFirst(val);
+                } else {
+                    list.add(val);
+                }
+                TreeNode left = tree.left;
+                TreeNode right = tree.right;
+                if (left != null) {
+                    queue.add(left);
+                }
+                if (right != null) {
+                    queue.add(right);
+                }
+            }
+            flag = !flag;
+            System.out.println(list);
+        }
+    }
+}
+
+class TreeNode {
+    int val;
+    TreeNode left;
+    TreeNode right;
+
+    TreeNode(int x) {
+        val = x;
+    }
+
+    public TreeNode(int val, TreeNode left, TreeNode right) {
+        this.val = val;
+        this.left = left;
+        this.right = right;
+    }
+}
+```