C++ 文件重定向与STL 完全指南

#include <cstdio>
#include <iostream>
using namespace std;
int main() {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    int a, b;
    cin >> a >> b;        // 自动从文件读
    cout << a + b << endl; // 自动写入文件
    return 0;
}

#include <fstream>
#include <iostream>
using namespace std;
int main() {
    ifstream fin("input.txt");   // 代替cin
    ofstream fout("output.txt"); // 代替cout
    int a, b;
    fin >> a >> b;
    fout << a + b << endl;
    fin.close(); fout.close();
    return 0;
}

#include <algorithm>
#include <iostream>
using namespace std;
int main() {
    int a = 10, b = 20;
    cout << min(a, b) << endl;  // 10
    cout << max(a, b) << endl;  // 20
    swap(a, b);  // a=20, b=10
    cout << min({3,1,4,1,5}) << endl; // 1
    cout << max({3,1,4,1,5}) << endl; // 5
    return 0;
}

#include <algorithm>
#include <vector>
#include <string>
#include <iostream>
using namespace std;
struct Stu { string name; int score; };
int main() {
    // 1. 数组升序
    int arr[] = {5,2,8,1};
    sort(arr, arr + 4);

// 2. vector升序
    vector<int> v = {5,2,8,1};
    sort(v.begin(), v.end());

// 3. 降序
    sort(v.begin(), v.end(), greater<int>());

// 4. 结构体按成绩降序
    vector<Stu> stu = {{"A",85},{"B",92},{"C",78}};
    sort(stu.begin(), stu.end(),
         [](const Stu& a, const Stu& b){
             return a.score > b.score;
         });
    for(auto& s : stu)
        cout << s.name << " " << s.score << endl;
    return 0;
}

#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
int main() {
    int n; cin >> n;
    vector<int> v(n);
    for(int i = 0; i < n; i++) cin >> v[i];

sort(v.begin(), v.end());

cout << "min=" << v.front() << endl;
    cout << "max=" << v.back() << endl;
    cout << "排序: ";
    for(int x : v) cout << x << " ";
    cout << endl;
    return 0;
}

#include <stack>
#include <iostream>
using namespace std;
int main() {
    stack<int> s;
    s.push(10); s.push(20); s.push(30);
    cout << s.top() << endl;  // 30
    s.pop();                  // 弹出30（不返回值！）
    cout << s.top() << endl;  // 20
    cout << s.size() << endl; // 2
    cout << s.empty() << endl;// 0(false)
    return 0;
}

#include <queue>
#include <iostream>
using namespace std;
int main() {
    queue<int> q;
    q.push(10); q.push(20); q.push(30);
    cout << q.front() << endl; // 10(队首)
    cout << q.back() << endl;  // 30(队尾)
    q.pop();                   // 弹出队首10
    cout << q.front() << endl; // 20
    cout << q.size() << endl;  // 2
    return 0;
}

#include <stack>
#include <string>
#include <iostream>
using namespace std;
bool isValid(string s) {
    stack<char> st;
    for(char c : s) {
        if(c=='(' || c=='[' || c=='{') {
            st.push(c);       // 左括号入栈
        } else {
            if(st.empty()) return false;
            char top = st.top();
            st.pop();
            if(c==')' && top!='(') return false;
            if(c==']' && top!='[') return false;
            if(c=='}' && top!='{') return false;
        }
    }
    return st.empty(); // 栈空=全匹配
}
int main() {
    string s; cin >> s;
    cout << (isValid(s) ? "YES" : "NO") << endl;
    return 0;
}

#include <vector>
#include <algorithm>
#include <iostream>
using namespace std;
int main() {
    vector<int> v;
    v.push_back(10);  // {10}
    v.push_back(20);  // {10,20}
    v.push_back(30);  // {10,20,30}
    v.pop_back();     // {10,20}
    v[0] = 100;      // 下标访问
    cout << v.size() << endl; // 2
    sort(v.begin(), v.end());
    for(int x : v) cout << x << " ";
    v.clear();
    return 0;
}

#include <list>
#include <iostream>
using namespace std;
int main() {
    list<int> lst = {3,1,4,1,5};
    lst.push_front(0);  // 头部插入
    lst.sort();           // 自带排序
    lst.unique();         // 去重
    for(int x : lst) cout << x << " ";
    // 0 1 3 4 5
    return 0;
}

#include <cstdio>
#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
int main() {
    freopen("data.in", "r", stdin);
    freopen("data.out", "w", stdout);
    int n; cin >> n;
    vector<int> v(n);
    long long sum = 0;
    for(int i = 0; i < n; i++) {
        cin >> v[i];
        sum += v[i];
    }
    sort(v.begin(), v.end());
    cout << "max=" << v.back() << endl;
    cout << "min=" << v.front() << endl;
    cout << "avg=" << (double)sum / n << endl;
    return 0;
}

#include <cstdio>
#include <algorithm>
#include <vector>
#include <string>
#include <iostream>
using namespace std;
struct Stu { string name; int score; };
int main() {
    freopen("score.in", "r", stdin);
    freopen("score.out", "w", stdout);
    int n; cin >> n;
    vector<Stu> stu(n);
    for(int i = 0; i < n; i++)
        cin >> stu[i].name >> stu[i].score;
    sort(stu.begin(), stu.end(),
         [](const Stu& a, const Stu& b) {
             return a.score > b.score;
         });
    for(int i = 0; i < n; i++)
        cout << i+1 << ". " << stu[i].name
             << " " << stu[i].score << endl;
    return 0;
}

#include <queue>
#include <iostream>
using namespace std;
int main() {
    queue<int> q;
    int m; cin >> m;
    while(m--) {
        int op; cin >> op;
        if(op == 1) {
            int id; cin >> id;
            q.push(id);
            cout << "入队:" << id << endl;
        } else if(op == 2) {
            if(!q.empty()) {
                cout << "叫号:" << q.front() << endl;
                q.pop();
            } else cout << "空" << endl;
        } else {
            cout << "等待:" << q.size() << endl;
        }
    }
    return 0;
}

#include <stack>
#include <iostream>
using namespace std;
int main() {
    int n; cin >> n;
    if(n == 0) { cout << 0 << endl; return 0; }
    stack<int> st;
    while(n > 0) {
        st.push(n % 2);  // 余数入栈
        n /= 2;
    }
    while(!st.empty()) {
        cout << st.top(); // 弹出=逆序输出
        st.pop();
    }
    cout << endl;
    return 0;
}

#include <cstdio>
#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
int main() {
    // 文件重定向（提交时注释掉）
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);

int n; cin >> n;
    vector<int> a(n);
    for(int i = 0; i < n; i++) cin >> a[i];

sort(a.begin(), a.end());

for(int x : a) cout << x << " ";
    cout << endl;
    return 0;
}