Count and Say

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本文介绍了一种特殊的整数序列——计数与描述序列，并提供了一个C++实现方案，用于生成该序列的第n项。序列从1开始，每一项都是对前一项的描述。

The count-and-say sequence is the sequence of integers beginning as follows:
1, 11, 21, 1211, 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, generate the nth sequence.

Note: The sequence of integers will be represented as a string.

class Solution {
public:
    string countAndSay(int n) {
        string s="1";
        for(int i=1;i!=n;++i){
            s = countAns(s);
        }
        return s;
    }
    string countAns(string s){
        int k =s.size();
        char ch = s[0];
        int count = 0;
        string ss;
        for(int i = 0;i<k;i++){
            if(ch==s[i]){
                count++;
            }else{
                ss.push_back('0'+count);
                ss.push_back(ch);
                count = 1;
                ch = s[i];
            }
        }
        ss.push_back('0'+count);
        ss.push_back(ch);
        return ss;
    }
};