zigzag print

dai · dai · commit 0f3ca10b1370 · 2021-03-31T15:15:17.000+08:00
diff --git a/26-算法面试专题-二叉树.md b/26-算法面试专题-二叉树.md
@@ -561,6 +561,52 @@ public class TreeSolvingUtil {
         System.out.println();
     }
 
+
+    /**
+     * 6、二叉树，zigzag打印
+     *
+     * @param root 根节点
+     * @return
+     */
+
+    public static List<List<Integer>> zigzagLevelOrder(TreeNode root) {
+        List<List<Integer>> ans = new ArrayList<>();
+        if (root == null) {
+            return ans;
+        }
+        LinkedList<TreeNode> deque = new LinkedList<>();
+        deque.add(root);
+        int size = 0;
+        // 开关每次切换，打印顺序每次变化
+        boolean isHead = true;
+        while (!deque.isEmpty()) {
+            size = deque.size();
+            List<Integer> curLevel = new ArrayList<>();
+            for (int i = 0; i < size; i++) {
+                TreeNode cur = isHead ? deque.pollFirst() : deque.pollLast();
+                curLevel.add(cur.val);
+                if(isHead) {
+                    if (cur.left != null) {
+                        deque.addLast(cur.left);
+                    }
+                    if (cur.right != null) {
+                        deque.addLast(cur.right);
+                    }
+                }else {
+                    if (cur.right != null) {
+                        deque.addFirst(cur.right);
+                    }
+                    if (cur.left != null) {
+                        deque.addFirst(cur.left);
+                    }
+                }
+            }
+            ans.add(curLevel);
+            isHead = !isHead;
+        }
+        return ans;
+    }
+
     /**
      * 7、二叉树，给定量给节点，求这两个节点的最近公共祖先
      *
