stable_sort和lambda表达式实现稳定排序

#include <bits/stdc++.h>
using namespace std;

int main() {
    string s;
    getline(cin, s);
    string s2;
    for (char c : s) {
        if (isalpha(c)) s2 += c;
    }
    stable_sort(s2.begin(), s2.end(),
    [] (char c1, char c2) {return tolower(c1) < tolower(c2);});
    size_t idx = 0;
    for (char c : s) {
        if (isalpha(c)) {
            cout << s2[idx++];
        } else {
            cout << c;
        }
    }
    cout << endl;
}