力扣222 完全二叉树的节点个数

class Solution {public int countNodes(TreeNode root) {if(root == null) return 0;TreeNode leftnode = root.left;int leftdepth = 0;TreeNode rightnode = root.right;int rightdepth = 0;while(leftnode != null) {leftnode = leftnode.left;leftdepth++;}while(rightnode != null) {rightnode = rightnode.right;rightdepth++;}if(rightdepth == leftdepth) return (2 << rightdepth) - 1;else {int leftnum = countNodes(root.left);int rightnum = countNodes(root.right);return 1 + leftnum + rightnum;}}
}

力扣111 二叉树的最小深度

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

力扣104 二叉树的最大深度

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