103. 二叉树的锯齿形层序遍历

Author: houfachao

src/main/java/com/geekidentity/leetcode/n0103/ZigzagLevelOrder.java

@@ -0,0 +1,43 @@
+package com.geekidentity.leetcode.n0103;
+
+import java.util.*;
+
+public class ZigzagLevelOrder {
+    public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
+        List<List<Integer>> result = new ArrayList<>();
+        if (root == null) return result;
+        Queue<TreeNode> nodeQueue = new ArrayDeque<TreeNode>();
+        nodeQueue.offer(root);
+        boolean left = true;
+        while (!nodeQueue.isEmpty()) {
+            int size = nodeQueue.size();
+            Deque<Integer> levelQueue = new LinkedList<>();
+            for (int i = 0; i < size; i++) {
+                TreeNode node = nodeQueue.poll();
+                if (left) {
+                    levelQueue.addLast(node.val);
+                } else {
+                    levelQueue.addFirst(node.val);
+                }
+                if (node.left != null) nodeQueue.offer(node.left);
+                if (node.right != null) nodeQueue.offer(node.right);
+            }
+            left = !left;
+            result.add(new LinkedList<>(levelQueue));
+        }
+        return result;
+    }
+
+    static class TreeNode {
+      int val;
+      TreeNode left;
+      TreeNode right;
+      TreeNode() {}
+      TreeNode(int val) { this.val = val; }
+      TreeNode(int val, TreeNode left, TreeNode right) {
+          this.val = val;
+          this.left = left;
+          this.right = right;
+      }
+  }
+}