[LeetCode] Count and Say

最新推荐文章于 2019-08-14 16:27:56 发布

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本文介绍了一种特殊的整数序列——计数与描述序列，并提供了一个C++实现方案来生成该序列的第n项。计数与描述序列从1开始，后续每一项都是对其前一项的描述。

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[Problem]

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 n^th sequence.

Note: The sequence of integers will be represented as a string.

[Solution]

class Solution {
public:
    string countAndSay(int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        // n <= 0
        if(n <= 0)return "";
   
        // n > 0
        int i = 0, count = 0;
        char pre;
        string res = "1", tmp = "";
   
        // count and say
        while(--n){
            // init
            tmp = "";
            pre = res[0];
            count = 1;
            i = 1;
   
            // count
            while(res[i] != '\0'){
                if(res[i] != pre){
                    tmp += (char)('0' + count);
                    tmp += pre;
                    count = 0;
                }
                pre = res[i];
                count++;
                i++;
            }
   
            // be careful the last one
            if(count > 0){
                tmp += (char)('0' + count);
                tmp += pre;
            }
   
            // replace
            res = tmp;
        }
        return res;
    }
};