Leetcode: 38. Count and Say

Description

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.

思路

• 注意题意求得时第n个
• 第n个是第n-1个的返回值的读出来的表达形式，把这个关系理解好了，就没问题了

代码

class Solution {
public:
    string countAndSay(int n) {
       if(n == 1) return "1";
       
       else return getSay(countAndSay(n - 1));
    }
    
    string getSay(const string& str){
        string res;
        int len = str.size();
        int count = 1;
        for(int i = 1; i < len; ++i){
            if(str[i] == str[i - 1]){
                count++;
                continue;
            }
            else{
                res += to_string(count) + str[i - 1];
                count = 1;
            }
        }
        
        res += to_string(count) + str[len - 1];
        
        return res;
    }
};