Leetcode 222 number of nodes of complete binary tree

Ideas

Original link

1. Method 1 ： Using recursion , as follows
2. Method 2 ： Use the classic solution , Sequence traversal , To count the number of nodes

class Solution {
    
    //  General recursive solution 
    public int countNodes(TreeNode root) {
    
        if(root == null) {
    
            return 0;
        }
        return countNodes(root.left) + countNodes(root.right) + 1;
    }
}

	// Use iterative algorithm 
class Solution {
    
    public int countNodes(TreeNode root) {
    
        if(root == null) return 0;
        Queue<TreeNode> que = new LinkedList<TreeNode>();
        que.add(root);
        int num = 0;
        while(!que.isEmpty()){
    
            int size = que.size();
            while(size > 0){
    
                TreeNode node = que.poll();
                if(node.left != null) que.add(node.left);
                if(node.right != null) que.add(node.right);
                num++;
                size--;
            }
        }
        return num;
    }
}