feat: 2025-10-31打卡

103.binary-tree-zigzag-level-order-traversal.java

@@ -25,35 +25,32 @@ class Solution {
         if(root == null) {
             return new ArrayList<>();
         }
-        LinkedList<TreeNode> queue = new LinkedList<>();
-        ArrayList<TreeNode> stack = new ArrayList<>();
-        queue.add(root);
+        boolean reverse = false;
         List<List<Integer>> ret = new ArrayList<>();
-        List<Integer> curLayer = new ArrayList<>();
-        TreeNode lastLayerNode = null, curLayerNode;
+        LinkedList<TreeNode> queue = new LinkedList<>();
+        queue.add(root);
+        TreeNode layerEndNode = null, curNode = null;
+        List<Integer> cache = new ArrayList<>();
         while(!queue.isEmpty()) {
             TreeNode tmp = queue.pollFirst();
-            curLayer.add(tmp.val);
+            cache.addLast(tmp.val);
             if(tmp.left != null) {
-                // queue.add(tmp.left);
-                stack.addLast(tmp.left);
+                queue.addLast(tmp.left);
+                curNode = tmp.left;
             }
             if(tmp.right != null) {
-                // queue.add(tmp.right);
-                stack.addLast(tmp.right);
+                queue.addLast(tmp.right);
+                curNode = tmp.right;
             }
-            if(tmp == lastLayerNode || lastLayerNode == null) {
-                // while()
-                // ret.add(curLayer);
-                // curLayer = new ArrayList<>();
-                // lastLayerNode = curLayerNode;
-                while(!stack.isEmpty()) {
-                    curLayerNode = stack.pollLast();
-                    queue.add(curLayerNode);
+            if(layerEndNode == null || layerEndNode == tmp) {
+                layerEndNode = curNode;
+                if(reverse) {
+                    ret.add(cache.reversed());
+                } else {
+                    ret.add(cache);
                 }
-                lastLayerNode = curLayerNode;
-                ret.add(curLayer);
-                curLayer = new ArrayList<>();
+                cache = new ArrayList<>();
+                reverse = !reverse;
             }
         }
         return ret;