Excel Sheet Column Number Solutions in C++

// Source : https://oj.leetcode.com/problems/excel-sheet-column-number/
// Author : Hao Chen
// Date   : 2014-12-29




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


string base26_int2str(long long n) {
    string ret;
    while(n>0){
        char ch = 'A' + (n-1)%26;
        ret.insert(ret.begin(), ch  );
        n -= (n-1)%26;
        n /= 26;
    }
    return ret;
}

long long base26_str2int(string& s){
    long long ret=0;
    for (int i=0; i<s.size(); i++){
        int n = s[i] - 'A' + 1;
        ret = ret*26 + n;
    }
    return ret;
}


string titleToNumber(int n) {
    return base26_str2int(n);
}

int main(int argc, char**argv)
{
    long long n = 27; 
    if (argc>1){
        n = atoll(argv[1]);
    }
    string ns = base26_int2str(n);
    n = base26_str2int(ns);

    cout << n << " = " << ns << endl;


    ns = "ABCDEFG";
    if (argc>2){
        ns = argv[2];
    }
    cout << ns << " = " << base26_str2int(ns) << endl;
}

/// Source : https://leetcode.com/problems/excel-sheet-column-number/description/
/// Author : liuyubobobo
/// Time   : 2018-08-30

#include <iostream>
#include <cmath>

using namespace std;


/// 26-based number
/// Time Complexity: O(len(s))
/// Space Complexity: O(1)
class Solution {
public:
    int titleToNumber(string s) {

        int num = 0;
        for(char c: s)
            num = num * 26 + (c - 'A' + 1);

        return num;
    }
};


int main() {

    cout << Solution().titleToNumber("A") << endl;  // 1
    cout << Solution().titleToNumber("AB") << endl; // 28
    cout << Solution().titleToNumber("ZY") << endl; // 701

    return 0;
}