tree

Author: rchen102

Java/leetcode 958.java

@@ -0,0 +1,31 @@
+class Solution {
+    public boolean isCompleteTree(TreeNode root) {
+        if (root == null) return true;
+        Queue<TreeNode> queue = new LinkedList<>();
+        queue.offer(root);
+        int prevShould = 1;
+        int prev = -1;
+        while (!queue.isEmpty()) {
+            int size = queue.size();
+            if (prev > 0) {
+                if (prev != prevShould) return false;
+                prevShould *= 2;
+            }
+            prev = size;
+            
+            boolean start = false;
+            for (int i = 0; i < size; i++)  {
+                TreeNode cur = queue.poll();
+                if (cur != null) {
+                    if (start) return false;
+                    queue.offer(cur.left);
+                    queue.offer(cur.right);
+                }
+                else {
+                    start = true;
+                }
+            }
+        } 
+        return true;
+    }
+}