Count and Say Solutions in C++

// Source : https://oj.leetcode.com/problems/count-and-say/
// Author : Hao Chen
// Date   : 2014-07-03



#include <stdlib.h>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
using namespace std;

string vecToStr(vector<int> v) {
    stringstream ss;
    for (int i=0; i<v.size(); i++) {
        ss << v[i]; 
    }
    return ss.str();
}

vector<int> getNext(vector<int>& v) {
    int cnt=0;
    int val=0;
    vector<int> ret;
    for(int i=0; i<v.size(); i++){
        if (i==0){
            val = v[i];
            cnt = 1;
            continue;
        }
        if (v[i] == val){
            cnt++;
        }else{
            ret.push_back(cnt); 
            ret.push_back(val); 
            val = v[i];
            cnt = 1;
        }
    }
    if (cnt>0 && val>0){
        ret.push_back(cnt); 
        ret.push_back(val); 
    }
    return ret;
}
    

string countAndSay(int n) {
    if (n<=0) return "";
    if (n==1) return "1";

    string s;
    vector<int> v;
    v.push_back(1);
    for(int i=2; i<=n; i++){
       v = getNext(v);
       //s = s + ", " +vecToStr(v);
    }
    s = vecToStr(v);
    return s;
}


int main(int argc, char** argv)
{
    int n = 4;
    if (argc>1){
        n = atoi(argv[1]);
    }
    cout << countAndSay(n) << endl;
    
    return 0;
}

#include <string>
using std::string;

class Solution {
public:
    string countAndSay(int n) {
        string ret{"1"};
        for (int i=0; i<n-1; ++i) {
            string str;
            auto b = ret.cbegin();
            for (auto e=b; e != ret.cend(); ++e)
                if (*b != *e) { str += std::to_string(e-b) + *b; b = e; }
            ret = str + std::to_string(ret.cend()-b) + *b;
        }
        return ret;
    }
};

/// Source : https://leetcode.com/problems/count-and-say/description/
/// Author : liuyubobobo
/// Time   : 2018-10-03

#include <iostream>

using namespace std;


/// Simulation
/// Time Complexity: O(n * 2^n)
/// Space Complexity: O(2^n)
class Solution {
public:
    string countAndSay(int n) {

        string s = "1";
        if(n == 1)
            return s;

        for(int i = 2; i <= n; i ++)
            s = next(s);
        return s;
    }

private:
    string next(const string& s){

        string ret = "";
        int start = 0;
        for(int i = start + 1; i <= s.size(); i ++)
            if(i == s.size() || s[i] != s[start]){
                ret += to_string(i - start) + s[start];
                start = i;
            }
        return ret;
    }
};


int main() {

    cout << Solution().countAndSay(1) << endl;
    cout << Solution().countAndSay(2) << endl;
    cout << Solution().countAndSay(3) << endl;
    cout << Solution().countAndSay(4) << endl;
    cout << Solution().countAndSay(5) << endl;
    cout << Solution().countAndSay(30) << endl;

    return 0;
}