leetcode 038 Count and Say

最新推荐文章于 2020-07-19 21:55:04 发布

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本文介绍了一种特殊的整数序列——计数并说序列，并提供了一个递归算法实现。该算法通过读出前一项的数字及连续出现次数来生成序列的下一项。

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.

#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
using namespace std;

class Solution {
public:
	string countAndSay(int n) {
		
		if(n == 0) return NULL;

		if(n==1) {
			return "1";
		}

		string ret = countAndSay(n-1);
		string ans = "";
		int len = ret.length();

		char pre = ret[0], count = '1';

		for(int i=1; i < len; i++) {
			if(ret[i] == pre) {
				count++;
			} else {
				ans=ans+count+pre;
				count = '1';
				pre = ret[i];
			}
		}

		ans = ans+count+pre;

		return ans;
	}
}