decode string

a.cpp

#include <iostream>
#include <vector>
#include <algorithm>
#include <unordered_map>
#include <string>
using namespace std;

string intToBytes(unsigned int a) {
    unsigned char mask = 0xff;
    string ret;
    for (int i = 0; i < 4; i++) {
        unsigned char temp = a & mask;
        ret += temp;
        a >>= 8;
    }
    return ret;
}

unsigned int bytesToInt(string s) {
    unsigned int ret = 0;
    for (int i = 3; i >= 0; i--) {
        unsigned char temp = s[i];
        ret |= temp;
        if (i != 0) {
            ret <<= 8;
        }
    }
    return ret;
}

// Encodes a list of strings to a single string.
string encode(vector<string>& strs) {
    string ret;
    for (int i = 0; i < strs.size(); i++) {
        ret += intToBytes(strs[i].size());
        cout << strs[i] << endl;
        ret += strs[i];
        cout << ret << endl;
    }
    return ret;
}

// Decodes a single string to a list of strings.
vector<string> decode(string s) {
    vector<string> ret;
    if (s == "")    return ret;
    unsigned int index = 0;
    while (index < s.size()) {
        unsigned int length = bytesToInt(s.substr(index, 4));
        index += 4;
        if (length != 0) {
            string temp = s.substr(index, length);
            ret.push_back(temp);
            index += length;
        } else {
            ret.push_back("");
        }
    }
    return ret;
}

int main() {
    vector<string> v = {"nSM","Dsy"};
    
    string a = encode(v);
    cout << a.size() << endl;
    cout << a << endl;
    for (int i = 0; i < a.size(); i++) {
        printf("%d : %d\n", i, a[i]);
    }
    
    vector<string> b = decode(a);
    
    return 0;
}