LeetCodeOJ. Count and Say

試題請參見: https://oj.leetcode.com/problems/count-and-say/

題目概述

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.

解題思路

簡單的模擬題, 在當前位"向後看", 是否有與當前位相同的連續數字.

如果有, 則計數. 計數完成後, 將下標移動至下一個(不同的)數字.

源代碼

class Solution {
public:
    std::string countAndSay(int n) {
        std::string previous = "1";
        
        for ( int i = 1; i < n; ++ i ) {
            std::string current;
            size_t step = 1;
            
            for ( size_t j = 0; j < previous.size(); j += step ) {
                char currentDigit = previous.at(j);
                step = 1;

                for ( size_t k = j + 1; k < previous.size() && previous.at(k) == previous.at(j); ++ k ) {
                    ++ step;
                }
                current += static_cast<char>(step + '0');
                current += currentDigit;
            }
            previous = current;
        }
        return previous;
    }
};