letterCombinationsOfAPhoneNumber.cpp

// Source : https://oj.leetcode.com/problems/letter-combinations-of-a-phone-number/
// Author : Hao Chen
// Date   : 2014-07-17

/********************************************************************************** 
* 
* Given a digit string, return all possible letter combinations that the number could represent.
* 
* A mapping of digit to letters (just like on the telephone buttons) is given below.
* 
* Input:Digit string "23"
* Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
* 
* Note:
* Although the above answer is in lexicographical order, your answer could be in any order you want.
* 
*               
**********************************************************************************/

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

vector<string> letterCombinations(string digits) {
    char  phone[10][4]={ {' ',  '\0', '\0', '\0' }, //0
                         {'\0', '\0', '\0', '\0' }, //1
                         {'a',  'b',  'c',  '\0' }, //2
                         {'d',  'e',  'f',  '\0' }, //3
                         {'g',  'h',  'i',  '\0' }, //4
                         {'j',  'k',  'l',  '\0' }, //5
                         {'m',  'n',  'o',  '\0' }, //6
                         {'p',  'q',  'r',  's'  }, //7
                         {'t',  'u',  'v',  '\0' }, //8
                         {'w',  'x',  'y',  'z'  }  //9
                       };

    vector<string> result;
    if (digits.size()<=0){
        result.push_back("");
        return result;
    }
    for( int i=0; i<digits.size(); i++ ) {
        if (!isdigit(digits[i])) {
            vector<string> r;
            return r;
        } 
        int d = digits[i] - '0';
        if (result.size()<=0){
            for( int j=0; j<4 && phone[d][j]!='\0'; j++ ){
                string s;
                s += phone[d][j];
                result.push_back(s);
            }
            continue;
        }
        vector<string> r;
        for (int j=0; j<result.size(); j++){
            for( int k=0; k<4 && phone[d][k]!='\0'; k++ ){
                string s = result[j] + phone[d][k];
                //sort(s.begin(), s.end());
                r.push_back(s); 
            }
        }
        result = r;
    }
    //sort(result.begin(), result.end());

    return result; 
}

void printVector(vector<string>& ss){
    cout << "{ ";
    for(int i=0; i<ss.size(); i++){
        if (i>0) cout << ", "; 
        cout << ss[i];
    }
    cout << " }" << endl;
}

int main(int argc, char**argv)
{
    string s="23";
    if (argc>1){
        s=argv[1];
    }
    vector<string> ss = letterCombinations(s);
    printVector(ss);
    return 0;
}