Count and Say

题目

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 n^th sequence.

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

思路

用迭代的方法：

class Solution {
public:
    string countAndSay(int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(n<1) return "";
        string p="1";
        string q="";
        int count=1;
        for(int i=2;i<=n;i++) {
            q="";
            for(int j=0;j<p.length();j++) {
                char ch=p[j];
                count=1;
                while(j+1<p.length() && p[j+1]==ch){
                    count++;
                    j++;
                }
                char cou='0'+count;
                q=q+cou+ch;
            }
            p=q;  
        }          
        return p;      
    }
};

附加：C++ 中int，char，string，CString类型转换

（1）在C标准库里面，string 转 int，使用atoi：

string text = "152";  

int number = std::atoi( text.c_str() );

（2）string 转 char * 

char *p = string.c_str();

......