Leetcode 模擬 Count and Say

Leetcode 模擬 Count and Say

Count and Say

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.

題意：有一個整數序列 1,11,21,1211,111221,...
它是這樣產生的：
1讀作 ‘one 1’，即 11
11讀作 'two 1s'，即 21
21讀作 'one 2 one 1'，即1211
...
給定整數 n，返回該序列的第 n 個數
思路：模擬
復雜度：時間O(n)，空間O(1)

//一般寫法
string countAndSay(int n){
	string last = "1";
	while(--n){
		int count = 1;
		char c = last[0];
		string cur;
		for(int i = 1; i <= last.size(); ++i){
			if(i < last.size() && last[i] == c) count++;
			else{
				cur += count + '0';
				cur += c;
				if(i < last.size()){
					count = 1;
					c = last[i];
				}
			}
		}
		last = cur;
	}
	return last;
}
//使用stl
string countAndSay(int n){
	string past = "1";
	while(--n){
		string cur;
		for(auto iter = past.begin(); iter != past.end();){
			auto iter2 = find_if(iter, past.end(), bind1st(not_equal_to(), *iter));
			cur += distance(iter, iter2) + '0';
			cur += *iter;
			iter = iter2;
		}
		past = cur;
	}
	return past;
}