number-of-students-unable-to-eat-lunch_1700.py

# 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

# ---------------------------------------Runtime 52 ms Beats 26.56% Memory 16.3 MB Beats 27.51%---------------------------------------

from typing import List


# My solution
class Solution:
    def countStudents(self, students: List[int], sandwiches: List[int]) -> int:
        i = j = 0
        while students:
            if students[i] == sandwiches[j]:
                students.pop(i)
                sandwiches.pop(j)
            elif sandwiches[j] not in students:
                return len(students)
            else:
                students.append(students.pop(i))
        return len(students)


# Solution @lee215
import collections

# Complexity
# Time O(n)
# Space O(2)


class Solution:
    def countStudents(self, A, B):
        count = collections.Counter(A)
        n, k = len(A), 0
        while k < n and count[B[k]]:
            count[B[k]] -= 1
            k += 1
        return n - k