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481.hpp
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481.hpp
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#ifndef LEETCODE_481_HPP
#define LEETCODE_481_HPP
#include <iostream>
#include <queue>
#include <algorithm>
#include <vector>
#include <unordered_map>
#include <unordered_set>
#include <set>
#include <numeric>
#include <stack>
#include <string>
using namespace std;
/*
A magical string S consists of only '1' and '2' and obeys the following rules:
The string S is magical because concatenating the number of
contiguous occurrences of characters '1' and '2' generates the string S itself.
The first few elements of string S is the following: S = "1221121221221121122……"
If we group the consecutive '1's and '2's in S, it will be:
1 22 11 2 1 22 1 22 11 2 11 22 ......
and the occurrences of '1's or '2's in each group are:
1 2 2 1 1 2 1 2 2 1 2 2 ......
You can see that the occurrence sequence above is the S itself.
Given an integer N as input, return the number of '1's in the first N number in the magical string S.
*/
class Solution {
public:
int magicalString(int n) {
string s = "122";
int i = 2;
while (s.size() < n) {
if (s[i] == '1')
s.push_back('1' + '2' - s.back());
else {
char c = '1' + '2' - s.back();
s.push_back(c);
s.push_back(c);
}
i++;
}
int cnt = 0;
for (int j = 0; j < n; ++j) {
if (s[j] == '1')
cnt++;
}
return cnt;
}
};
#endif //LEETCODE_481_HPP