【算法第十四天7.28】二叉树的最大深度，二叉树的最小深度 ，完全二叉树的节点个数

思路

class Solution {public int maxDepth(TreeNode root) {if(root == null) return 0;if(root.left == null) return maxDepth(root.right) + 1;if(root.right == null) return maxDepth(root.left) + 1;int max = Math.max(maxDepth(root.left),maxDepth(root.right));return max + 1;}
}

思路

class Solution {public int minDepth(TreeNode root) {if(root == null) return 0;if(root.left == null) return minDepth(root.right) + 1;if(root.right == null) return minDepth(root.left) +1;int min = Math.min(minDepth(root.left),minDepth(root.right));return min + 1;}
}

思路

class Solution {public int countNodes(TreeNode root) {if(root == null) return 0;return countNodes(root.left) + countNodes(root.right) + 1;// if(root == null) return 0;// // 层序用队列！！！！！// Queue<TreeNode> queue = new LinkedList<>();// queue.offer(root);// // 总结点个数// int res = 0;// while(!queue.isEmpty()){//     int size = queue.size();//     while(size-- > 0){//         TreeNode node = queue.poll();//         // 每一层的循环都用res++上//         res++;//         if(node.left != null) queue.offer(node.left);//         if(node.right != null) queue.offer(node.right);//     }// }// return res;}
}