LeetCode 038 Count and Say

题目要求：Count and Say

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.

分析：

看了半天才看懂这道题……

代码如下：

class Solution {
public:
    string countAndSay(int n) {
        
        string s("1");
        
        while(--n)
            s = getNext(s);
            
        return s;
    }
    
    string getNext(const string &s){
        stringstream ss;
        
        for(auto i = s.begin(); i != s.end(); ){
            auto j = find_if(i, s.end(), bind1st(not_equal_to<char>(), *i));
            
            //几个i，核心
            ss << distance(i, j) << *i;
            i = j;
        }
        
        return ss.str();
    }
};