Movie Theatres - Amazon Top Interview Questions

Problem Statement :

Given a list of time exclusive intervals for different movie showings (possibly overlapping), find the minimum number of theatres required to be able to show all movies.


0 ≤ n ≤ 100,000 where n is the length of `intervals

Example 1


intervals = [
    [30, 75],
    [0, 50],
    [60, 150]




[30, 75] and [0, 50] overlap. [30, 75] and [60, 150] also overlap but later on. So the max number here is 2.

Example 2


intervals = [
    [10, 20],
    [20, 30]




Boundaries are exclusive so these intervals are not considered overlapping.

Example 3


intervals = [
    [0, 1],
    [0, 1],
    [0, 1]




The three intervals happen all at the same time so we need 3.

Solution :


                        Solution in C++ :

int solve(vector<vector<int>> &intervals) {
    map<int, int> m;
    for (auto &i : intervals) {
        m[i[0]] += 1;
        m[i[1]] -= 1;
    int ans = 0, prev = 0;
    for (auto &[x, y] : m) {
        ans = max(ans, prev += y);
    return ans;

                        Solution in Python : 
class Solution:
    def solve(self, intervals):
        events = []
        OPEN, CLOSE = 1, 0
        # bit of a hack to keep proper sort order, for example [[10, 20], [20, 30]]. We want to prioritize open over close as the answer should be 1

        for i, (start, end) in enumerate(intervals):
            events.append((start, OPEN, i))
            events.append((end, CLOSE, i))

        window = set()
        ans = 0

        for event_time, event_type, idx in events:
            if event_type == OPEN:

            ans = max(ans, len(window))
        return ans

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