代码随想录day16 ● 104.二叉树的最大深度 559.n叉树的最大深度 ● 111.二叉树的最小深度 ● 222.完全二叉树的节点个数

104. 二叉树的最大深度

迭代法：

 1 class Solution {
 2 public:
 3     int maxDepth(TreeNode* root) {
 4         //创建变量用于存储深度
 5         int ans = 0;
 6         queue<TreeNode*> que;
 7         if (root !=  nullptr) que.push(root);
 8         while (!que.empty()){
 9             int size = que.size();
10             while (size--){
11                 TreeNode* node = que.front();
12                 que.pop();
13                 if (node->left) que.push(node->left);
14                 if (node->right) que.push(node->right);
15             }
16             ans++;
17         }
18         return ans;
19     }
20 };

递归法：

 1 class Solution {
 2 public:
 3     int getdepth(TreeNode* node){
 4         if (node == nullptr) return 0;
 5         int leftdepth = getdepth(node->left);
 6         int rightdepth = getdepth(node->right);
 7         int depth = 1 + max(leftdepth, rightdepth);
 8         return depth;
 9     }
10 
11     int minDepth(TreeNode* root) {
12         return getdepth(root);
13     }
14 };

111. 二叉树的最小深度

 1 class Solution {
 2 public:
 3     int minDepth(TreeNode* root) {
 4         int result = 0;
 5         queue<TreeNode*> que;
 6         if (root != nullptr) que.push(root);
 7         while (!que.empty()){
 8             int size = que.size();
 9             result++;
10             while (size--){
11                 TreeNode* node = que.front();
12                 que.pop();
13                 if (node->left == nullptr && node->right == nullptr){
14                     return result;
15                 }
16                 if (node->left) que.push(node->left);
17                 if (node->right) que.push(node->right);
18             }
19         }
20         return result;
21     }
22 };

222. 完全二叉树的节点个数

 1 class Solution {
 2 public:
 3     int countNodes(TreeNode* root) {
 4         queue<TreeNode*> que;
 5         if (root != NULL) que.push(root);
 6         int result = 0;
 7         while (!que.empty()) {
 8             int size = que.size();
 9             for (int i = 0; i < size; i++) {
10                 TreeNode* node = que.front();
11                 que.pop();
12                 result++;   // 记录节点数量
13                 if (node->left) que.push(node->left);
14                 if (node->right) que.push(node->right);
15             }
16         }
17         return result;
18     }
19 };