solutions/0038-count-and-say/count-and-say.cpp

// The count-and-say sequence is the sequence of integers with the first five terms as following:
//
//
// 1.     1
// 2.     11
// 3.     21
// 4.     1211
// 5.     111221
//
//
// 1 is read off as "one 1" or 11.
// 11 is read off as "two 1s" or 21.
// 21 is read off as "one 2, then one 1" or 1211.
//
// Given an integer n where 1 ≤ n ≤ 30, generate the nth term of the count-and-say sequence. You can do so recursively, in other words from the previous member read off the digits, counting the number of digits in groups of the same digit.
//
// Note: Each term of the sequence of integers will be represented as a string.
//
//  
//
// Example 1:
//
//
// Input: 1
// Output: "1"
// Explanation: This is the base case.
//
//
// Example 2:
//
//
// Input: 4
// Output: "1211"
// Explanation: For n = 3 the term was "21" in which we have two groups "2" and "1", "2" can be read as "12" which means frequency = 1 and value = 2, the same way "1" is read as "11", so the answer is the concatenation of "12" and "11" which is "1211".
//
//


class Solution {
public:
    string countAndSay(int n) {
        string *s1=new string("1");
        for(int i=1;i!=n;++i){
            string *s2 = new string();
            auto it=s1->begin();
            for(auto jt=it;jt<=s1->end();++jt)if(jt==s1->end() or *it!=*jt){
                s2->append(to_string(jt-it));
                s2->push_back(*it);
                it=jt;
            }
            delete s1;
            s1=s2;
        }
        return *s1;
    }
};