Create 0958-check-completeness-of-a-binary-tree.js

Author: aadil42

javascript/0958-check-completeness-of-a-binary-tree.js

@@ -0,0 +1,82 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * Time O(n) | Space O(n)
+ * LevelOrder traversal | BFS
+ * https://leetcode.com/problems/check-completeness-of-a-binary-tree/
+ * @param {TreeNode} root
+ * @return {boolean}
+ */
+var isCompleteTree = function(root) {
+    
+    // get the depth of the tree
+    // bfs until n-1 level of depth
+
+    const getDepth = (node) => {
+        if(!node) return 0;
+        return 1 + Math.max(getDepth(node.left), getDepth(node.right));
+    }
+    
+    const depth = getDepth(root) - 1;
+
+    const q = new Queue();
+    q.enqueue(root);
+
+    const checkLastLevel = (arr) => {
+        while(arr[arr.length - 1] === null) arr.pop();
+
+        let i = 0;
+        while(i < arr.length) {
+            if(arr[i] === null) return false;
+            i++;
+        }
+
+        return true;
+    }
+
+    let i = 0;
+    while(i < depth) {
+
+        let size = q.size();
+
+        if(size !== 2**i) return false;
+
+        while(size) {
+            const node = q.dequeue();
+            if(!node.left && i !== depth-1) return false;
+            if(!node.right && i !== depth-1) return false;
+
+            if(i !== depth - 1){
+                q.enqueue(node.left);
+                q.enqueue(node.right);
+            } else {
+
+                if(!node.left) {
+                    q.enqueue(null);
+                } else {
+                    q.enqueue(node.left);
+                }
+
+                if(!node.right) {
+                    q.enqueue(null);
+                }  else {
+                    q.enqueue(node.right);
+                }
+
+            }
+            
+            size--;
+        }
+
+        i++;
+    }
+
+
+    return checkLastLevel(q.toArray());
+};