38. Count and Say 计数和读法

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, generate the nth term of the count-and-say sequence.

Note: Each term of the sequence of integers will be represented as a string.

Example 1:

Input: 1
Output: "1"

Example 2:

Input: 4
Output: "1211"

Difficulty: Easy

这道题的意思为 :

  • 从1开始将当前的数字转化为口语对应的数字,比如1读作1个1,记作11.
  • 11读作2个1,记作21
  • 21读作1个2,1个1,记作1211

class Solution {
public:
    string countAndSay(int n) {
        if (n==0) return "";
        string res = "1";
        while (--n){
            string cur = "";
            for (int i=0;i<res.size();i++){
                int count = 1;
                while (i+1<res.size() && res[i]==res[i+1]){
                    count ++;
                    i++;
                }
                cur += to_string(count) + res[i];
            }
            res = cur;
        }
        return res;
    }
};

参考资料

https://leetcode.com/problems/count-and-say/discuss/16043/c-solution-easy-understand

 
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