38. Count and Say

题目

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"

解析

• 主要就是迭代的思想，主要当前重复的元素个数和重复的元素值。

// add 38. Count and Say
class Solution_38 {
public:
	string countAndSay(int n) {
		if (n<=0)
		{
			return "";
		}
		string res="1";
		for (int i = 1; i < n;i++) //依次迭代n-1次
		{
			string temp = "";
			int cnt = 1;
			for (int j = 1; j < res.length();j++)
			{
				if (res[j-1]==res[j])
				{
					cnt++;
				}
				else
				{
					temp.push_back(cnt + '0'); //相同元素的个数
					temp.push_back(res[j-1]); //相同的元素是什么！
					cnt = 1; //元素个数复位
				}
			}
			temp.push_back(cnt + '0');
			temp.push_back(res[res.length()-1]); //最后一个元素
			res = temp;//重新赋值下一轮迭代值
		}

		return res;
	}
};

题目来源

• leetcode 38. Count and Say