main.cpp

// Source: https://leetcode.com/problems/number-of-students-unable-to-eat-lunch
// Title: Number of Students Unable to Eat Lunch
// Difficulty: Easy
// Author: Mu Yang <http://muyang.pro>

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// The school cafeteria offers circular and square sandwiches at lunch break, referred to by numbers `0` and `1` respectively. All students stand in a queue. Each student either prefers square or circular sandwiches.
//
// The number of sandwiches in the cafeteria is equal to the number of students. The sandwiches are placed in a **stack**. At each step:
//
// - If the student at the front of the queue **prefers** the sandwich on the top of the stack, they will **take it** and leave the queue.
// - Otherwise, they will **leave it** and go to the queue's end.
//
// This continues until none of the queue students want to take the top sandwich and are thus unable to eat.
//
// You are given two integer arrays `students` and `sandwiches` where `sandwiches[i]` is the type of the `i^th` sandwich in the stack (`i = 0` is the top of the stack) and `students[j]` is the preference of the `j^th` student in the initial queue (`j = 0` is the front of the queue). Return the number of students that are unable to eat.
//
// **Example 1:**
//
// ```
// Input: students = [1,1,0,0], sandwiches = [0,1,0,1]
// Output: 0
// Explanation:
// - Front student leaves the top sandwich and returns to the end of the line making students = [1,0,0,1].
// - Front student leaves the top sandwich and returns to the end of the line making students = [0,0,1,1].
// - Front student takes the top sandwich and leaves the line making students = [0,1,1] and sandwiches = [1,0,1].
// - Front student leaves the top sandwich and returns to the end of the line making students = [1,1,0].
// - Front student takes the top sandwich and leaves the line making students = [1,0] and sandwiches = [0,1].
// - Front student leaves the top sandwich and returns to the end of the line making students = [0,1].
// - Front student takes the top sandwich and leaves the line making students = [1] and sandwiches = [1].
// - Front student takes the top sandwich and leaves the line making students = [] and sandwiches = [].
// Hence all students are able to eat.
// ```
//
// **Example 2:**
//
// ```
// Input: students = [1,1,1,0,0,1], sandwiches = [1,0,0,0,1,1]
// Output: 3
// ```
//
// **Constraints:**
//
// - `1 <= students.length, sandwiches.length <= 100`
// - `students.length == sandwiches.length`
// - `sandwiches[i]` is `0` or `1`.
// - `students[i]` is `0` or `1`.
//
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

#include <algorithm>
#include <queue>
#include <stack>
#include <vector>

using namespace std;

// Simulation
class Solution {
 public:
  int countStudents(vector<int>& students, vector<int>& sandwiches) {
    auto que = queue<int>();
    for (auto student : students) que.push(student);
    reverse(sandwiches.begin(), sandwiches.end());

    auto skipCount = 0;
    while (!que.empty()) {
      auto curr = que.front();
      que.pop();

      if (curr == sandwiches.back()) {
        sandwiches.pop_back();
        skipCount = 0;
      } else {
        que.push(curr);
        ++skipCount;
      }

      if (skipCount == que.size()) break;
    }

    return que.size();
  }
};