[代码随想录] 第十四天

222.完全二叉树的节点个数[https://leetcode.cn/problems/count-complete-tree-nodes/submissions/498293461/]
思路：递归法

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

思路：迭代法

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 * int val;
 * TreeNode left;
 * TreeNode right;
 * TreeNode() {}
 * TreeNode(int val) { this.val = val; }
 * TreeNode(int val, TreeNode left, TreeNode right) {
 * this.val = val;
 * this.left = left;
 * this.right = right;
 * }
 * }
 */
class Solution {
    public int countNodes(TreeNode root) {
        int x = 0;
        if (root == null) {
            return 0;
        }
        Queue<TreeNode> que = new LinkedList<>();
        que.offer(root);
        while (!que.isEmpty()) {
            List<Integer> list = new ArrayList<>();
            int loop = que.size();
            for (int i = 0; i < loop; i++) {
                TreeNode temp = que.poll();

                if (temp.left != null) {
                    que.offer(temp.left);
                }
                if (temp.right != null) {
                    que.offer(temp.right);
                }
                x++;
            }
        }
        return x;
    }
}

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104.二叉树的最大深度[https://leetcode.cn/problems/maximum-depth-of-binary-tree/submissions/498058606/]
思路：递归法。迭代法在第十三天的博客中。

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

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111.二叉树的最小深度[https://leetcode.cn/problems/minimum-depth-of-binary-tree/]
思路：递归法。迭代法在第十三天的博客中。

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 Math.min(leftDepth, rightDepth) + 1;
        }else if(root.left==null && root.right!=null){
            return rightDepth + 1;
        }else {
            return leftDepth + 1;
        }    
    }  
}