感谢大佬的帮忙，就下面这道题啊啊啊啊

#include <iostream>
#include <string>
#include <vector>
#include <stdlib.h>

using namespace std;
int main() {
    string str;
    cout << "请输入:";
    cin >> str;
    int len = str.size();
    // 1.20.30.12.3.5.7.4.6.100
    vector<string> vec;
    int cursor = -1;
    while (cursor < len) {
        int index = cursor + 1;
        cursor = str.find('.', cursor + 1);
        if (cursor < 0) {
            vec.push_back(str.substr(index));
            break;
        }
        vec.push_back(str.substr(index, cursor - index));
    }
    if (vec.size() < 3) {
        cout << '(' << str << ")";
        return 0;
    }
    int markIndex = -1;
    int count = 1;
    for (int i = 1; i < vec.size() - 1; i++) {
        int vec0 = atoi(vec[i-1].c_str());
        int vec1 = atoi(vec[i].c_str());
        int vec2 = atoi(vec[i+1].c_str());
        int cmp_res = (vec0- vec1) * (vec1 - vec2);
        if (markIndex < 0) {
            if (cmp_res > 0) {
                markIndex = i-1;
                count += 2;
            } else {
                cout << '(' << vec[i-1] << '.' << vec[i] << ").";
                markIndex = -1;
                count = 1;
            }
        } else if(cmp_res > 0) {
            count++;
        } else {
            cout << '(';
            for (int j = markIndex; j < markIndex + count; j++) {
                cout << vec[j];
                if(j < markIndex + count - 1) {
                    cout << '.';
                }
            }
            cout << ").";
            markIndex = -1;
            count = 1;
        }
        if (i == vec.size() -2) {
            if (markIndex < 0) {
                cout << '(' << vec[i] << '.' << vec[i+1] << ')';
            } else {
                cout << '(';
                for (int j = markIndex; j < markIndex + count; j++) {
                    cout << vec[j];
                    if(j < markIndex + count - 1) {
                        cout << '.';
                    }
                }
                cout << ")";
            }
        }
    }
    return 0;
}