number_of_students_unable_to_eat_lunch.py

# https://leetcode.com/problems/number-of-students-unable-to-eat-lunch/description/
# 1700. Number of Students Unable to Eat Lunch

# 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.

from collections import Counter
from typing import List

class Solution:
    def countStudents(self, students: List[int], sandwiches: List[int]) -> int:
        ''' Number of Students Unable to Eat Lunch '''
        hungry = 0
        while len(students) > hungry:
            if students[0] == sandwiches[0]:
                sandwiches.pop(0)
                hungry = 0
            else:
                students.append(students[0])
                hungry+=1
            students.pop(0)
        return len(students)
    def countStudentsEx(self, students: List[int], sandwiches: List[int]) -> int:
        ''' Number of Students Unable to Eat Lunch '''
        cnt = Counter(students)
        for v in sandwiches:
            if cnt[v] == 0:
                return cnt[v ^ 1]
            cnt[v] -= 1
        return 0

print(Solution().countStudents([1,1,0,0], [0,1,0,1]))
# Output: 0 
print(Solution().countStudents([1,1,1,0,0,1], [1,0,0,0,1,1]))
# Output: 3
print(Solution().countStudents([0,0,0,1,1,0], [1,0,0,0,1,1]))
# Output: 1
print(Solution().countStudents([0,0,0,1,1,0], [0,1,1,1,0,0]))
# Output: 3

print(Solution().countStudentsEx([1,1,0,0], [0,1,0,1]))
# Output: 0 
print(Solution().countStudentsEx([1,1,1,0,0,1], [1,0,0,0,1,1]))
# Output: 3
print(Solution().countStudentsEx([0,0,0,1,1,0], [1,0,0,0,1,1]))
# Output: 1
print(Solution().countStudentsEx([0,0,0,1,1,0], [0,1,1,1,0,0]))
# Output: 3