1700. Number of Students Unable to Eat Lunch

Number of Students Unable to Eat Lunch

Problem Description

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.

Let`s code it!

/**
 * @param {number[]} students
 * @param {number[]} sandwiches
 * @return {number}
 */
var countStudents = function(students, sandwiches) {
    let round = 0;
    while (true) {
        // run till all students able to eat or round is equal to length of students
        if (students.length == 0 || round == students.length){
            break;
        }
        if (students[0] != sandwiches[0]) {
            students.push(students.shift());
            round++;
        } else {
            students.shift();
            sandwiches.shift();
            round = 0;
        }
    }
    return students.length;
};




Runtime: 107 ms, faster than 23.18% of JavaScript online submissions for Number of Students Unable to Eat Lunch.
Memory Usage: 41.8 MB, less than 86.36% of JavaScript online submissions for Number of Students Unable to Eat Lunch.

Complexity analysis.

Time Complexity

We are traversing through the complete array + rounds which needs O(NlogN).

Space Complexity

We are using a contact store round, hence space complexity is O(1).

Resources:

https://github.com/PraveenMistry/leetCode

https://medium.com/@praveenmistry/queue-javascript-part-2-5dab626110aa

Conclusion

That’s all folks! In this post, we solved LeetCode problem #1700. Number of Students Unable to Eat Lunch

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You can find the complete source code on my GitHub repository. If you like what you learn. feel free to fork 🔪 and star ⭐ it.

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Happy coding!