LeetCode----count-and-say

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题目描述

The count-and-say sequence is the sequence of integers beginning as follows:
1, 11, 21, 1211, 111221, ...

1is read off as"one 1"or11.
11is read off as"two 1s"or21.
21is read off as"one 2, thenone 1"or1211.

Given an integer n, generate the nth sequence.

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

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注意题目是求整个序列的第N项，而每一项是其前一项的解释！！！

class Solution {
public:
    string countAndSay(int n) {
        //题意：求序列的第n项（每一项是其前一项的‘解释’）
        string res("1");//第一项
​
        if (n==1)
            return res;
        for (int i=2; i<=n; ++i){
            int len = res.size();
            int count = 1;
            string temp="";//用于运行中暂存当前项结果
            for (int j=0; j<len; ++j){
                if (j!=len-1){
                    if (res[j] ==res[j+1]){
                        count++;
                    }
                    else {
                        
                        temp += to_string(count);
                        temp += res[j];
                        count = 1;
                    }
                }else {
                    
                    temp += to_string(count);
                    temp += res[j];
                }
            }
            res = temp;//更新当前项结果
        }
        return res;
    }
};

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