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Find minimum number of Laptops required

Last Updated : 11 Apr, 2023
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There are N jobs and the start and finish times of the jobs are given in arrays start[] and end[] respectively. Each job requires one laptop and laptops can’t be shared. Find the minimum number of laptops required given that you can give your laptop to someone else when you are not doing your job.

Examples:

Input: N = 3, start[] = {1, 2, 3}, end[] = {4, 4, 6}
Output: 3
Explanation: We can clearly see that everyone’s supposed to be doing their job at time 3. So, 3 laptops will be required at minimum.

Input: N = 3, start[] = {1, 5, 2}, end[] = {2, 6, 3}
Output: 1
Explanation: All jobs can be done using 1 laptop only.

Approach: This can be solved with the following idea:

We need to determine the bare minimum of laptops needed to complete the task. If we look closely, our objective may be reduced to the issue of needing to locate the most laptops possible at any one time.
Here, the idea of a different array can be used. Here, we’ll indicate the start and end times using a hash map rather than an array.

Steps involved in the implementation of code:

  • The start and end times of utilizing the laptop will be marked on a hash map in step one.
  • Repeat Step 1 while iterating through the start and end arrays. When we try to store the number of laptops currently use, we will increase the hash value of start[i] by 1 and decrease the hash value of end[i] by 1.
  • Third Step: We must employ a hash map data structure that is always sorted.
  • We’ll keep a variable called “maxx” that stores the most laptops we might possibly need at any given time.
  • Repeat the hash map iteratively, marking the beginning and ending points as +1 and -1, respectively. Maintain called cnt that represents the number of laptops that are currently in use.
  • Add the hash map value to cnt and compare it to maxx after each iteration.

Below is the implementation of the above approach:

C++




// C++ code for the above approach:
#include <bits/stdc++.h>
using namespace std;
 
// Function to calculate number of
// laptops required
int minLaptops(int N, vector<int>& start, vector<int>& end)
{
 
    // Create an unordered_map to store the
    // start and end times of each
    // event and how many times they occur
    unordered_map<int, int> map;
 
    // Iterate over the start
    // times and increment their
    // count in the unordered_map
    for (int i = 0; i < N; i++) {
 
        if (map.count(start[i]))
            map[start[i]]++;
        else
            map[start[i]] = 1;
    }
 
    // Iterate over the end times
    // and decrement their count
    // in the unordered_map
    for (int i = 0; i < N; i++) {
 
        if (map.count(end[i]))
            map[end[i]]--;
        else
            map[end[i]] = -1;
    }
 
    // Create a 2D vector to store
    // the start and end times along
    // with their counts
    vector<vector<int> > res(2 * N, vector<int>(2, 0));
 
    // Iterate over the unordered_map
    // and populate the 2D vector
    int ind = 0;
 
    for (auto val : map) {
        res[ind][0] = val.first;
        res[ind][1] = val.second;
        ind++;
    }
 
    // Sort the 2D vector first by
    // start time, then by end time
    // (to break ties)
    sort(res.begin(), res.end(),
         [](const vector<int>& a, const vector<int>& b) {
             if (a[0] == b[0])
                 return a[1] < b[1];
             else
                 return a[0] < b[0];
         });
 
    // Initialize counters for the number
    // of laptops needed and the
    // maximum number of laptops needed
    int c = 0, ans = 0;
 
    // Iterate over the sorted 2D vector
    // and update the laptop counters
    for (int i = 0; i < 2 * N; i++) {
        c += res[i][1];
        ans = max(ans, c);
    }
 
    // Return the maximum number
    // of laptops needed
    return ans;
}
 
// Driver code
int main()
{
 
    // Sample inputs
    int N = 3;
    vector<int> start = { 1, 2, 3 };
    vector<int> end = { 4, 4, 6 };
 
    // Function call
    int minLaptopsRequired = minLaptops(N, start, end);
 
    // Print the output
    cout << minLaptopsRequired << endl;
 
    return 0;
}
// This code is contributed by prasad264


Java




// Java code for the above approach:
import java.util.*;
class GFG {
 
    // Function to calculate number of
    // laptops required
    public static int minLaptops(int N, int[] start,
                                 int[] end)
    {
 
        // Create a HashMap to store the
        // start and end times of each
        // event and how many times
        // they occur
        HashMap<Integer, Integer> map = new HashMap<>();
 
        // Iterate over the start times
        // and increment their
        // count in the HashMap
        for (int i = 0; i < N; i++) {
 
            if (map.containsKey(start[i]))
                map.put(start[i], map.get(start[i]) + 1);
            else
                map.put(start[i], 1);
        }
 
        // Iterate over the end times and
        // decrement their count
        // in the HashMap
        for (int i = 0; i < N; i++) {
 
            if (map.containsKey(end[i]))
                map.put(end[i], map.get(end[i]) - 1);
            else
                map.put(end[i], -1);
        }
 
        // Create a 2D array to store the
        // start and end times along
        // with their counts
        int[][] res = new int[2 * N][2];
 
        // Iterate over the HashMap and
        // populate the 2D array
        int ind = 0;
 
        for (Map.Entry<Integer, Integer> val :
             map.entrySet()) {
            res[ind][0] = val.getKey();
            res[ind][1] = val.getValue();
            ind++;
        }
 
        // Sort the 2D array first by start
        // time, then by end time
        // (to break ties)
        Arrays.sort(
            res, Comparator.<int[]>comparingInt(a -> a[0])
                     .thenComparingInt(a -> a[1]));
 
        // Initialize counters for the
        // number of laptops needed and the
        // maximum number of laptops needed
        int c = 0, ans = 0;
 
        // Iterate over the sorted 2D array
        // and update the laptop counters
        for (int i = 0; i < 2 * N; i++) {
            c += res[i][1];
            ans = Math.max(ans, c);
        }
 
        // Return the maximum number
        // of laptops needed
        return ans;
    }
 
    // Driver code
    public static void main(String[] args)
    {
 
        // Sample inputs
        int N = 3;
        int[] start = { 1, 2, 3 };
        int[] end = { 4, 4, 6 };
 
        // Function call
        int minLaptops = minLaptops(N, start, end);
 
        // Print the output
        System.out.println(minLaptops);
    }
}


Python3




# Python3 code for the above approach
 
from collections import defaultdict
 
# Function to calculate number of laptops required
 
 
def min_laptops(N, start, end):
    # Create a dictionary to store the start and end times of each event and how many times they occur
    d = defaultdict(int)
 
    # Iterate over the start times and increment their count in the dictionary
    for i in range(N):
        d[start[i]] += 1
 
    # Iterate over the end times and decrement their count in the dictionary
    for i in range(N):
        d[end[i]] -= 1
 
    # Create a list of tuples to store the start and end times along with their counts
    res = []
    for key, value in d.items():
        res.append((key, value))
 
    # Sort the list of tuples first by start time, then by end time (to break ties)
    res.sort(key=lambda x: (x[0], x[1]))
 
    # Initialize counters for the number of laptops needed and the maximum number of laptops needed
    c, ans = 0, 0
 
    # Iterate over the sorted list of tuples and update the laptop counters
    for i in range(len(res)):
        c += res[i][1]
        ans = max(ans, c)
 
    # Return the maximum number of laptops needed
    return ans
 
 
# Driver code
if __name__ == '__main__':
    # Sample inputs
    N = 3
    start = [1, 2, 3]
    end = [4, 4, 6]
 
    # Function call
    min_laptops_required = min_laptops(N, start, end)
 
    # Print the output
    print(min_laptops_required)


C#




// C# code implementation
 
using System;
using System.Collections.Generic;
using System.Linq;
 
public class GFG {
 
    // Function to calculate number of laptops required
    public static int MinLaptops(int N, int[] start,
                                 int[] end)
    {
        // Create a Dictionary to store the start and end
        // times of each event and how many times they occur
        Dictionary<int, int> map
            = new Dictionary<int, int>();
 
        // Iterate over the start times and increment their
        // count in the Dictionary
        for (int i = 0; i < N; i++) {
            if (map.ContainsKey(start[i]))
                map[start[i]] = map[start[i]] + 1;
            else
                map[start[i]] = 1;
        }
 
        // Iterate over the end times and decrement their
        // count in the Dictionary
        for (int i = 0; i < N; i++) {
            if (map.ContainsKey(end[i]))
                map[end[i]] = map[end[i]] - 1;
            else
                map[end[i]] = -1;
        }
 
        // Create a 2D array to store the start and end
        // times along with their counts
        int[][] res = new int[2 * N][];
        for (int i = 0; i < res.Length; i++) {
            res[i] = new int[2];
        }
 
        // Iterate over the Dictionary and populate the 2D
        // array
        int ind = 0;
        foreach(KeyValuePair<int, int> val in map)
        {
            res[ind][0] = val.Key;
            res[ind][1] = val.Value;
            ind++;
        }
 
        // Sort the 2D array first by start time, then by
        // end time (to break ties)
        Array.Sort(res,
                   (a, b) = > a[0].CompareTo(b[0]) != 0
                                ? a[0].CompareTo(b[0])
                                : a[1].CompareTo(b[1]));
 
        // Initialize counters for the number of laptops
        // needed and the maximum number of laptops needed
        int c = 0, ans = 0;
 
        // Iterate over the sorted 2D array and update the
        // laptop counters
        for (int i = 0; i < 2 * N; i++) {
            c += res[i][1];
            ans = Math.Max(ans, c);
        }
 
        // Return the maximum number of laptops needed
        return ans;
    }
 
    static public void Main()
    {
 
        // Code
        // Sample inputs
        int N = 3;
        int[] start = { 1, 2, 3 };
        int[] end = { 4, 4, 6 };
 
        // Function call
        int minLaptops = MinLaptops(N, start, end);
 
        // Print the output
        Console.WriteLine(minLaptops);
    }
}
 
// This code is contributed by karthik.


Javascript




function minLaptops(N, start, end) {
  // Create an object to store the start and end times of each event
  // and how many times they occur
  let map = {};
 
  // Iterate over the start times and increment their count in the object
  for (let i = 0; i < N; i++) {
    if (map[start[i]]) {
      map[start[i]]++;
    } else {
      map[start[i]] = 1;
    }
  }
 
  // Iterate over the end times and decrement their count in the object
  for (let i = 0; i < N; i++) {
    if (map[end[i]]) {
      map[end[i]]--;
    } else {
      map[end[i]] = -1;
    }
  }
 
  // Create a 2D array to store the start and end times along with their counts
  let res = Array(2 * N)
    .fill()
    .map(() => Array(2).fill(0));
 
  // Iterate over the object and populate the 2D array
  let ind = 0;
  for (let [key, value] of Object.entries(map)) {
    res[ind][0] = parseInt(key);
    res[ind][1] = value;
    ind++;
  }
 
  // Sort the 2D array first by start time, then by end time (to break ties)
  res.sort((a, b) => {
    if (a[0] === b[0]) {
      return a[1] - b[1];
    } else {
      return a[0] - b[0];
    }
  });
 
  // Initialize counters for the number of laptops needed and the maximum number of laptops needed
  let c = 0;
  let ans = 0;
 
  // Iterate over the sorted 2D array and update the laptop counters
  for (let i = 0; i < 2 * N; i++) {
    c += res[i][1];
    ans = Math.max(ans, c);
  }
 
  // Return the maximum number of laptops needed
  return ans;
}
 
// Sample inputs
let N = 3;
let start = [1, 2, 3];
let end = [4, 4, 6];
 
// Function call
let minLaptopsRequired = minLaptops(N, start, end);
 
// Print the output
console.log(minLaptopsRequired);


Output

3

Time Complexity:  O(N*logN)
Auxiliary Space: O(N) 



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