38. Count and Say

38. 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.

Analysis:

不复杂，主要是依次判断当前digit和上一个digit是否相同。

Source Code（C++）:

#include <iostream>
#include <string>
#include <map>
#include <vector>
using namespace std;

class Solution {
public:
string countAndSay(int n) {
string s="1";
for (int i=0; i<n-1; i++) {  //第一个已经求出，只需要循环n-1次即可
int index=0;
int same_digit_counts=0;
string next_string;
while(index < s.size())
{
if (index == 0)
{
same_digit_counts=1;
}
else if (s.at(index) == s.at(index-1))
{
same_digit_counts++;
}
else {
next_string.push_back(char(same_digit_counts+'0'));
next_string.push_back(s.at(index-1));
same_digit_counts=1;
}
index++;
}
next_string.push_back(char(same_digit_counts+'0'));
next_string.push_back(s.at(index-1));
s=next_string;
}
return s;
}
};

int main() {
Solution sol;
cout << sol.countAndSay(5);
return 0;
}