C++ string 类 与相关函数

#include <iostream>
#include <string>
#include <cctype>
using namespace std;
string toLower(string s){
    for(char &c : s) c = tolower(c);
    return s;
}
int main(){
    string text, word;
    getline(cin, text);
    cin >> word;
    text = toLower(text);
    word = toLower(word);
    int cnt = 0, pos = 0;
    while((pos = text.find(word, pos)) != string::npos){
        cnt++;
        pos += word.size();
    }
    cout << cnt << endl;
    return 0;
}

#include <iostream>
#include <string>
using namespace std;
int main(){
    string s;
    getline(cin, s);
    for(char &c : s){
        if(isalpha(c)){
            if(c == 'z') c = 'a';
            else if(c == 'Z') c = 'A';
            else c++;
        }
    }
    cout << s << endl;
    return 0;
}

#include <iostream>
#include <string>
using namespace std;
int main(){
    string s;
    getline(cin, s);
    long long sum = 0, cur = 0;
    for(char c : s){
        if(isdigit(c)){
            cur = cur * 10 + (c - '0');
        } else {
            if(cur != 0){
                sum += cur;
                cur = 0;
            }
        }
    }
    if(cur != 0) sum += cur;  // 处理末尾数字
    cout << sum << endl;
    return 0;
}

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
int main(){
    string s;
    cin >> s;
    reverse(s.begin(), s.end());
    cout << s << endl;
    return 0;
}

#include <iostream>
#include <string>
#include <cctype>
using namespace std;
int main(){
    string s;
    getline(cin, s);
    int upper = 0, lower = 0, digit = 0;
    for(char c : s){
        if(isupper(c)) upper++;
        else if(islower(c)) lower++;
        else if(isdigit(c)) digit++;
    }
    cout << upper << " " << lower << " " << digit << endl;
    return 0;
}

#include <iostream>
#include <string>
using namespace std;
int main(){
    string a, b;
    cin >> a >> b;
    if(a < b) cout << a << endl;
    else cout << b << endl;
    return 0;
}

#include <iostream>
#include <string>
using namespace std;
int main(){
    string s;
    getline(cin, s);
    for(char &c : s){
        if(c == ' ') c = '*';
    }
    cout << s << endl;
    return 0;
}

#include <iostream>
#include <string>
using namespace std;
string toLower(string s){
    for(char &c : s) c = tolower(c);
    return s;
}
int main(){
    string text, word;
    getline(cin, text);
    cin >> word;
    text = toLower(text);
    word = toLower(word);
    int cnt = 0, pos = 0;
    while((pos = text.find(word, pos)) != string::npos){
        cnt++;
        pos += word.size();
    }
    cout << cnt << endl;
    return 0;
}

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
int main(){
    string s, t;
    cin >> s;
    t = s;
    reverse(t.begin(), t.end());
    cout << (s == t ? "YES" : "NO") << endl;
    return 0;
}

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
int main(){
    string a, b;
    cin >> a >> b;
    sort(a.begin(), a.end());
    sort(b.begin(), b.end());
    cout << (a == b ? "YES" : "NO") << endl;
    return 0;
}

#include <iostream>
#include <string>
using namespace std;
int main(){
    string op, s;
    int k;
    cin >> op >> s >> k;
    for(char &c : s){
        if(isalpha(c)){
            char base = isupper(c) ? 'A' : 'a';
            int offset = (op == "decrypt") ? -k : k;
            c = (char)((c - base + offset % 26 + 26) % 26 + base);
        }
    }
    cout << s << endl;
    return 0;
}

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
bool isPalin(string s){
    string t = s;
    reverse(t.begin(), t.end());
    return s == t;
}
int main(){
    string s, best = "";
    cin >> s;
    for(int i = 0; i < s.size(); i++)
        for(int j = i+1; j <= s.size(); j++){
            string sub = s.substr(i, j-i);
            if(isPalin(sub) && sub.size() > best.size())
                best = sub;
        }
    cout << best << endl;
    return 0;
}

#include <iostream>
#include <string>
#include <stack>
using namespace std;
int main(){
    string s;
    getline(cin, s);
    stack<char> st;
    for(char c : s){
        if(c == '(' || c == '[' || c == '{') st.push(c);
        else {
            if(st.empty()){
                cout << "NO" << endl;
                return 0;
            }
            char top = st.top();
            if((c==')' && top!='(') || (c==']' && top!='[') || (c=='}' && top!='{')){
                cout << "NO" << endl;
                return 0;
            }
            st.pop();
        }
    }
    cout << (st.empty() ? "YES" : "NO") << endl;
    return 0;
}

#include <iostream>
#include <string>
using namespace std;
int main(){
    string s, result = "";
    cin >> s;
    int cnt = 1;
    for(int i = 1; i <= s.size(); i++){
        if(i < s.size() && s[i] == s[i-1]){
            cnt++;
        } else {
            result += s[i-1] + to_string(cnt);
            cnt = 1;
        }
    }
    cout << result << endl;
    return 0;
}

#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main(){
    string s;
    int n;
    cin >> s >> n;
    if(n <= 1){ cout << s << endl; return 0; }
    vector<string> rows(n);
    int cur = 0, dir = 1;
    for(char c : s){
        rows[cur] += c;
        if(cur == 0) dir = 1;
        if(cur == n-1) dir = -1;
        cur += dir;
    }
    string result;
    for(auto &r : rows) result += r;
    cout << result << endl;
    return 0;
}