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2582-Pass_the_Pillow.cpp
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2582-Pass_the_Pillow.cpp
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/*******************************************************************************
* 2582-Pass_the_Pillow.cpp
* Billy.Ljm
* 06 July 2024
*
* =======
* Problem
* =======
* https://leetcode.com/problems/pass-the-pillow/
*
* There are n people standing in a line labeled from 1 to n. The first person
* in the line is holding a pillow initially. Every second, the person holding
* the pillow passes it to the next person standing in the line. Once the pillow
* reaches the end of the line, the direction changes, and people continue
* passing the pillow in the opposite direction.
*
* For example, once the pillow reaches the nth person they pass it to the
* (n - 1)th person, then to the (n - 2)th person and so on.
*
* Given the two positive integers n and time, return the index of the person
* holding the pillow after time seconds.
*
* ===========
* My Approach
* ===========
* We can just calculate the solution directly. The situation repeats after 2n-2
* time steps, so we take the time mod (2n-2) and find out who holds the pillow.
*
* This has a time complexity of O(1) and space complexity of O(1).
******************************************************************************/
#include <iostream>
#include <vector>
using namespace std;
/**
* << operator for vectors
*/
template <typename T>
std::ostream& operator<<(std::ostream& os, const std::vector<T>& v) {
os << "[";
for (const auto elem : v) {
os << elem << ",";
}
if (v.size() > 0) os << "\b";
os << "]";
return os;
}
/**
* Solution
*/
class Solution {
public:
int passThePillow(int n, int time) {
time = time % (2*n - 2);
if (time < n) return time + 1;
else return 2*n - 1 - time;
}
};
/**
* Test cases
*/
int main(void) {
Solution sol;
int n, time;
// test case 1
n = 4;
time = 5;
std::cout << "passThePillow(" << n << ", " << time << ") = ";
std::cout << sol.passThePillow(n, time) << std::endl;
// test case 2
n = 3;
time = 2;
std::cout << "passThePillow(" << n << ", " << time << ") = ";
std::cout << sol.passThePillow(n, time) << std::endl;
return 0;
}