Magical String Problem
Description
LeetCode Problem 481.
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 s is 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 is s itself.
Given an integer n, return the number of 1’s in the first n number in the magical string s.
Example 1:
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Input: n = 6
Output: 3
Explanation: The first 6 elements of magical string s is "122112" and it contains three 1's, so return 3.
Example 2:
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Input: n = 1
Output: 1
Constraints:
- 1 <= n <= 10^5
Sample C++ Code
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class Solution {
public:
int magicalString(int n) {
if (n < 1)
return 0;
queue<int> q;
int ans = 1, num = 1, count = 2, i = 3;
while (i < n) {
while (count--) {
q.push(num);
if (i < n && num == 1)
++ans;
++i;
}
num = (num == 1 ? 2 : 1);
count = q.front();
q.pop();
}
return ans;
}
};