樹的前中後序遍歷

最近發現，leetcode的除錯面板真是個神器，可以新增各種函式

最近想實現樹的三種遍歷，想想自己寫輸入輸出函式就累（對不起我不是合格程式設計師orz 嚶嚶嚶於是就到leetcode上抄了函式改了下，看了下實現方式其實也不是很難（站著說話ing））

#include <iostream>
#include <string>
#include <vector>
#include <stack>
#include <algorithm>
#include <queue>
#include
 
 <sstream>
using namespace std;
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
//[a,b,c,d,e,f,null,null,g]
struct TreeNode
{
    int val;
    TreeNode *
 
left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
class Solution
{
  public:
    vector<int> preorderTraversal(TreeNode *root)
    {
        vector<int> res;
        std::stack<TreeNode *> temp;
        while (root || !temp.empty())
        {
            while
 
 (root)
            {
                temp.push(root);
                res.push_back(root->val);
                root = root->left;
            }
            root = temp.top();
            temp.pop();
            root = root->right;
        }
        return res;
    }

    vector<int> inorderTraversal(TreeNode *root)
    {
        vector<int> res;
        std::stack<TreeNode *> temp;
        while (root || !temp.empty())
        {
            while (root)
            {
                temp.push(root);
                root = root->left;
            }
            root = temp.top();
            temp.pop();
            res.push_back(root->val);
            root = root->right;
        }
        return res;
    }
    vector<int> postorderTraversal(TreeNode *root)
    {
        vector<int> res;
        std::stack<TreeNode *> temp;
        while (root || !temp.empty())
        {
            while (root)
            {
                temp.push(root);
                res.insert(res.begin(), root->val);
                root = root->right;
            }
            root = temp.top();
            temp.pop();
            root = root->left;
        }
        return res;
    }
};

void trimLeftTrailingSpaces(string &input)
{
    input.erase(input.begin(), find_if(input.begin(), input.end(), [](int ch) {
                    return !isspace(ch);
                }));
}

void trimRightTrailingSpaces(string &input)
{
    input.erase(find_if(input.rbegin(), input.rend(), [](int ch) {
                    return !isspace(ch);
                })
                    .base(),
                input.end());
}

TreeNode *stringToTreeNode(string input)
{
    trimLeftTrailingSpaces(input);
    trimRightTrailingSpaces(input);
    input = input.substr(1, input.length() - 2);
    if (!input.size())
    {
        return nullptr;
    }

    string item;
    stringstream ss;
    ss.str(input);

    getline(ss, item, ',');
    TreeNode *root = new TreeNode(stoi(item));
    queue<TreeNode *> nodeQueue;
    nodeQueue.push(root);

    while (true)
    {
        TreeNode *node = nodeQueue.front();
        nodeQueue.pop();

        if (!getline(ss, item, ','))
        {
            break;
        }

        trimLeftTrailingSpaces(item);
        if (item != "null")
        {
            int leftNumber = stoi(item);
            node->left = new TreeNode(leftNumber);
            nodeQueue.push(node->left);
        }

        if (!getline(ss, item, ','))
        {
            break;
        }

        trimLeftTrailingSpaces(item);
        if (item != "null")
        {
            int rightNumber = stoi(item);
            node->right = new TreeNode(rightNumber);
            nodeQueue.push(node->right);
        }
    }
    return root;
}

string integerVectorToString(vector<int> list, int length = -1)
{
    if (length == -1)
    {
        length = list.size();
    }

    if (length == 0)
    {
        return "[]";
    }

    string result;
    for (int index = 0; index < length; index++)
    {
        int number = list[index];
        result += to_string(number) + ", ";
    }
    return "[" + result.substr(0, result.length() - 2) + "]";
}



int main(int argc, char const *argv[])
{
    string line;
    cout << "請輸入您的節點,以中括號開始和結束.如：[a,b,c,d,e,f,null,null,g](a到g代表數字).\n以#開頭表示退出." << endl;
    while (getline(cin, line))
    {
        if (line[0] == '#')
        {
            break;
        }
        TreeNode *root = stringToTreeNode(line);
        cout << "請選擇您要進行的操作" << endl;
        cout << "\t\t1.前序遍歷\n\t\t2.中序遍歷\n\t\t3.後序遍歷\n\t\t0.退出\n";
        while (getline(cin, line))
        {
            int choose=stoi(line);
            if (choose == 0)
            {
                break;
            }
            vector<int> ret;
            switch (choose)
            {
            case 1:
            {
                ret = Solution().preorderTraversal(root);
                break;
            }

            case 2:
            {
                ret = Solution().inorderTraversal(root);
                break;
            }

            case 3:
            {
                ret = Solution().postorderTraversal(root);
                break;
            }
            }
            string out = integerVectorToString(ret);
            cout << out << endl;
        }
    }
    system("pause");
    return 0;
}