Count and Say

最新推荐文章于 2024-12-21 10:31:21 发布

ray3044

最新推荐文章于 2024-12-21 10:31:21 发布

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分类专栏： Algorithm 文章标签： Interview Algorithm LeetCode String

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本文详细介绍了如何使用C++实现计数说数序列算法，包括核心逻辑、代码实现以及生成特定序列的方法。通过实例演示，帮助读者理解和掌握计数说数序列的生成过程。

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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.

class Solution {
public:
    string countAndSay(int n) {
        
        if (n < 1) {
            return "";
        }
        
        if (n == 1) {
            return "1";
        }
        
        std::string ret("1");
        for (int i = 2; i <= n; i++) {
            // we don't need another variable to record 
            // previous resulted string, as we have it 
            // as ret (previous result) and stringstream object
            // (current result)
            std::stringstream newStrSeq;
            char last = ret[0];
            int count = 0;
            
            // ret[ret.size()] == '\0'
            for (int j = 0; j <= ret.length(); j++) {
                if (ret[j] == last) {
                    count++;
                } else {
                    newStrSeq << count << last;
                    last = ret[j];
                    count = 1;
                }
            }
            
            ret = newStrSeq.str();
        }
        
        return ret;
    }
};