二叉树的遍历

前序遍历

• 遍历顺序：中，左，右

• 代码实现：

  void dfs(TreeNode* root) {
          if (root != nullptr)result.push_back(root->val);
          if (root->left != nullptr)dfs(root->left);
          if (root->right != nullptr)dfs(root->right);
      }
  

关于力扣144:

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vectorresult;
    void dfs(TreeNode* root) {
        if (root != nullptr)result.push_back(root->val);
        if (root->left != nullptr)dfs(root->left);
        if (root->right != nullptr)dfs(root->right);
    }
    vector preorderTraversal(TreeNode* root) {
        if (root == nullptr)return result;
        dfs(root);
        return result;
    }
};

中序遍历

• 遍历顺序：左，中，右

• 代码实现:

  void dfs(TreeNode* cur) {
          if (cur == nullptr)return;
          dfs(cur->left);
          result.push_back(cur->val);
          dfs(cur->right);
      }
  

关于力扣94：

class Solution {
public:
    vectorresult;
    void dfs(TreeNode* cur) {
        if (cur == nullptr)return;
        dfs(cur->left);
        result.push_back(cur->val);
        dfs(cur->right);
    }
    vector inorderTraversal(TreeNode* root) {
        if (root == nullptr)return result;
        dfs(root);
        return result;
    }
};

后序遍历

• 遍历顺序：左，右，中

• 代码实现：

  void dfs(TreeNode* cur) {
          if (cur == nullptr)return;
          dfs(cur->left);
          dfs(cur->right);
          result.push_back(cur->val);
      }
  

关于力扣145：

class Solution {
public:
    vectorresult;
    void dfs(TreeNode* cur) {
        if (cur == nullptr)return;
        dfs(cur->left);
        dfs(cur->right);
        result.push_back(cur->val);
    }
    vector postorderTraversal(TreeNode* root) {
        if (root == nullptr)return result;
        dfs(root);
        return result;
    }
};