leetcode144 递归前序遍历

前后中遍历的前后中，指的是中间节点。

• 前序遍历 ：中左右
• 后续遍历： 左右中
• 中序遍历： 左中右

/**
 * 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:
    void Traversal(TreeNode* cur , vector<int> &result)
    {
        if (cur == nullptr) return;
        result.push_back(cur->val);
        Traversal(cur->left , result);
        Traversal(cur->right , result);

    }

    vector<int> preorderTraversal(TreeNode* root) {

        vector<int> result;
        Traversal(root,result);
        return result;
    }
};

leetcode145 递归后序遍历

/**
 * 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:
    void traversal(TreeNode* cur , vector<int> &result)
    {
        if (cur == nullptr) return;
        traversal(cur->left , result);
        traversal(cur->right , result);
        result.push_back(cur->val);

    }
    vector<int> postorderTraversal(TreeNode* root) {
        vector<int> result;
        traversal(root, result);
        return result;
    }
};

leetcode94 递归中序遍历

/**
 * 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:
    void traversal(TreeNode* cur , vector<int> &result)
    {
        if(cur==nullptr) return;
        traversal( cur->left , result);
        result.push_back( cur->val);
        traversal( cur->right , result);
    }
    vector<int> inorderTraversal(TreeNode* root) {
        vector<int> result;
        traversal(root,result);
        return result;
    }
};

二刷

前序

/**
 * 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:
    vector<int> result;
    void back_track(TreeNode* cur)
    {
        if(cur == nullptr) return;
        result.push_back(cur->val);
        back_track(cur->left);
        back_track(cur->right);
    }
    vector<int> preorderTraversal(TreeNode* root) {
        back_track(root);
        return result;
    }
};

后序

/**
 * 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:
    vector<int> result;
    void back_track(TreeNode* cur)
    {
        if(cur == nullptr) return;
        back_track(cur->left);
        back_track(cur->right);
        result.push_back(cur->val);
    }
    vector<int> postorderTraversal(TreeNode* root) {
        back_track(root);
        return result;
    }
};

中序

/**
 * 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:
    vector<int> result;
    void back_track(TreeNode* cur)
    {
        if(cur == nullptr) return;
        back_track(cur->left);
        result.push_back(cur->val);
        back_track(cur->right);
    }
    vector<int> inorderTraversal(TreeNode* root) {
        back_track(root);
        return result;
    }
};