LeetCode 38. Count and Say

Posted 2020-08-09

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.

 

这个题目的意思要弄懂，我刚开始没看懂什么意思

1.1

2.11

3.21

4.1211

5.111221

count and say 就是这样输入1则输出1，第二行就有规律了，第一行是1个1，第二行的字符串就是1个1连起来11

同理第三行是2个1，第四行是1个2,1个1.。。。

弄懂了题目的意思，做起来就不会这么难了

class Solution {
public:
    string countAndSay(int n) {
        string pre = "1", current;
        for (int i = 2;i <= n;++i)
        {
            current = "";
            char prechar = pre[0];
            int count = 0;
            for (int j = 1;j < pre.size();++j)
            {
                ++count;
                if (pre[j] != prechar)
                {
                    current.insert(end(current), char(count + 48));
                    current.insert(end(current), prechar);
                    
                    prechar = pre[j];
                    count = 0;
                }
            }
            current.insert(end(current), char(count + 1 + 48));
            current.insert(end(current), prechar);
            pre = current;
        }
        return pre; 
    }
};