Any problem involving the traversal of a tree in a level-by-level order can be efficiently solved by using this approach. We will use a Queue to keep track of all the nodes of a level before we jump onto the next level. This also means that the space complexity of the algorithm will be O(W), where W is the maximum number of nodes on any level.
const levelNodes = [root];
while (levelNodes.length > 0) {
const levelLength = levelNodes.length;
for (let i = 0; i < levelLength; i++) {
const node = levelNodes.shift();
aggregateLevelNode(node);
if (node.left) {
levelNodes.push(node.left);
}
if (node.right) {
levelNodes.push(node.right);
}
}
}