24. 算法

24.1. 二叉树输入处理，包括建树、打印树、释放树。

include<iostream>
#include <queue>
#include<sstream> //istringstream
using namespace std;//结点
struct Node
{int val;Node* left;Node* right;Node() :val(0), left(nullptr), right(nullptr) {}; //空结点Node(int value):val(value), left(nullptr), right(nullptr) {}; //有值结点
};//使用字符串流用于分割字符串
//建二叉树
Node* buildTree(istringstream& iss)
{string token="";if (!(iss >> token) || token == "null") return nullptr; //字符串流是空或者null时，直接返回空指针Node* root = new Node(stoi(token)); //新建根结点并入队queue<Node*>Q;Q.push(root);while (iss >> token) //新建当前节点的左右节点{Node* node = Q.front();Q.pop();if (token != "null"){node->left = new Node(stoi(token));Q.push(node->left);}if (!(iss >> token))break;if (token != "null"){node->right = new Node(stoi(token));Q.push(node->right);}}return root;
}//释放二叉树
void deleteTree(Node* root)
{if (!root) return;deleteTree(root->left); //释放左子树deleteTree(root->right);//释放右子树delete root; //释放当前结点并置空root = nullptr;
}//打印二叉树-层次遍历
void display(Node* root)
{if (!root) return;queue<Node*>Q;Q.push(root);while (!Q.empty()){int n = Q.size();while (n--){auto node = Q.front();Q.pop();if (node) //如果结点存在，输出结点值并将左右结点入队{cout << node->val << " ";Q.push(node->left);Q.push(node->right);}else //如果结点不存在，输出nullcout << "null ";}cout << endl; //一层一行}}int main()
{/*string s = "1 2 3 4 5 null 6 7 null null null null 8";*/string s;getline(cin, s); //控制台输入字符串istringstream iss(s); Node* root = buildTree(iss); //建树display(root); //打印树deleteTree(root); //释放树return 0;
};

24.2. 单链表输入处理，包括建链（头插、尾插）、打印链、释放链。

istringstream 默认以空格作为分隔符来划分字符串，但可以使用 getline()指定分隔符。

#include<iostream>
#include<sstream>
using namespace std;//结点
struct Node
{int val;Node* next;Node() :val(0), next(nullptr) {}; //空结点Node(int value):val(value), next(nullptr) {}; //有值结点，尾插Node(int value, Node* next):val(value),next(next){} //有值结点，头插
};//建单链表-头插法
Node* insertHead(istringstream& iss)
{string token = "";if (!(getline(iss, token, ','))) return nullptr; //字符串流是空，直接返回空指针Node* head = new Node(stoi(token)); //新建第一个结点Node* cur = head;while (getline(iss, token, ',')) //新建其余结点cur = new Node(stoi(token),cur);return cur; //返回当前结点
}//建单链表-尾插法
Node* insertTail(istringstream& iss)
{string token="";if (!(getline(iss,token,','))) return nullptr; //字符串流是空，直接返回空指针Node* head = new Node(stoi(token)); //新建第一个结点Node* cur = head;while (getline(iss, token, ',')) //新建其余结点{cur->next= new Node(stoi(token));cur = cur->next;}return head; //返回第一个结点
}//释放单链表
void deleteList(Node* head)
{if (!head) return;while (head){auto cur = head;head = head->next;delete cur; //释放结点并置空cur = nullptr;}
}//打印单链表
void display(Node* head)
{if (!head) return;while (head){cout<<head->val<<" ";head = head->next;}cout <<endl;
}int main()
{/*string s = "[1,2,3,4]"*/string s;getline(cin, s); //控制台输入字符串s = s.substr(1, s.length() - 2); //去除首尾方括号istringstream iss(s);Node* head = insertTail(iss); //建链display(head); //打印链deleteList(head); //释放链return 0;
};

24.3. 一维矩阵输入处理。

#include<iostream>
#include <vector>
#include<sstream>
using namespace std;int main()
{string s = "[1,2,3,4]";//string s;//getline(cin, s); //控制台输入字符串s = s.substr(1, s.length() - 2); //去除首尾方括号istringstream iss(s); string token = "";vector<int>v;while (getline(iss, token, ','))//分割字符串并存放进数组v.emplace_back(stoi(token)); for (auto&& u : v) //打印数组cout << u << " ";return 0;
};

24.4. 二维矩阵输入处理。

可以使用嵌套的 std::istringstream。

#include<iostream>
#include <vector>
#include<sstream>
using namespace std;int main()
{string s = "[[1,3,5,7],[10,11,16,20],[23,30,34,60]]";//string s;//getline(cin, s); //控制台输入字符串s = s.substr(1, s.length() - 2); //去除首尾方括号istringstream iss(s);string token = "";vector<vector<int>>v;while (getline(iss, token, '[')) //以'['分割字符串，对应行{if (token.empty()) continue; //跳过空字符串istringstream in_iss(token);string in_token = "";vector<int>in_v;//如"7]"转7 是因为stoi()会提取开头的数字部分并将其转换为整数。while(getline(in_iss,in_token,',')) //以'，'分割字符串，对应列in_v.emplace_back(stoi(in_token));v.emplace_back(in_v); }for (auto&& in_v : v) //打印二维数组{for (auto&& u : in_v)cout << u << " ";cout << endl;}return 0;
};

24.5. 调用函数输入处理。

最小栈，设计一个支持 push ，pop ，top 操作，并能在常数时间内检索到最小元素的栈，实现 MinStack 类。

#include<iostream>
#include<stack>
#include<vector>
#include<sstream>
using namespace std;class MinStack {
private:stack<int>st,minst; //使用栈辅助检索最小元素public:MinStack() { minst.push(INT_MAX); }void push(int val) {//当前元素-对应栈中最小元素if (val < minst.top())minst.push(val);elseminst.push(minst.top());st.push(val);}void pop() {//同时出栈minst.pop();st.pop();}int top() { return st.top(); }int getMin() { return minst.top();}
};int main()
{string scall = R"( ["MinStack","push","push","push","getMin","pop","top","getMin"] )"; //R"()"是一种原始字符串字面量的写法。string snum = "[[],[-2],[0],[-3],[],[],[],[]]";//string scall,snum;//getline(cin, scall); //getline(cin,snum); //控制台输入字符串snum.erase(remove(snum.begin(), snum.end(), '['),snum.end()); snum.erase(remove(snum.begin(), snum.end(), ']'), snum.end()); //snum去除'['和']'istringstream iss(snum);string token = "";vector<int>v;while (getline(iss, token, ',')) //snum以','分割字符串并存放进数组{if (token.empty()) continue; //跳过空字符串v.emplace_back(stoi(token)); }scall = scall.substr(2, scall.length() - 4); //scall去除首"(["和尾"])"scall.erase(remove(scall.begin(), scall.end(), '"'), scall.end()); //scall去除'"'istringstream iss2(scall);int size = v.size(), i = 0;static MinStack minStack; //声明成静态，保证只初始化一次while (getline(iss2, token, ',')) //scall以','分割字符串并调用{if (token == "MinStack"){minStack = MinStack();cout << "null,";}else if (token == "push"){minStack.push(v[i++]);cout << "null,";}else if (token == "getMin"){cout << minStack.getMin() << ",";}else if (token == "pop"){minStack.pop();cout << "null,";}else if (token == "top"){cout<<minStack.top() << ",";}}return 0;
};