Find maximum meetings in one room

Difficulty Level : Medium
Last Updated : 28 Apr, 2021

There is one meeting room in a firm. There are N meetings in the form of (S[i], F[i]) where S[i] is the start time of meeting i and F[i] is finish time of meeting i. The task is to find the maximum number of meetings that can be accommodated in the meeting room. Print all meeting numbers

Examples:

Input : s[] = {1, 3, 0, 5, 8, 5}, f[] = {2, 4, 6, 7, 9, 9}
Output : 1 2 4 5
First meeting [1, 2]
Second meeting [3, 4]
Fourth meeting [5, 7]
Fifth meeting [8, 9]
Input : s[] = {75250, 50074, 43659, 8931, 11273, 27545, 50879, 77924},
f[] = {112960, 114515, 81825, 93424, 54316, 35533, 73383, 160252 }
Output : 6 7 1

Approach:
Idea is to solve the problem using the greedy approach which is the same as Activity Selection Problem.

Sort all pairs(Meetings) in increasing order of second number(Finish time) of each pair.
Select first meeting of sorted pair as the first Meeting in the room and push it into result vector and set a variable time_limet(say) with the second value(Finishing time) of the first selected meeting.
Iterate from the second pair to last pair of the array and if the value of the first element(Starting time of meeting) of the current pair is greater then previously selected pair finish time (time_limit) then select the current pair and update the result vector (push selected meeting number into vector) and variable time_limit.
Print the Order of meeting from vector.

Below is the implementation of the above approach.

C++

// C++ program to find maximum number of meetings
#include <bits/stdc++.h>
using namespace std;
 
// Structure for storing starting time,
// finishing time and position of meeting.
struct meeting {
    int start;
    int end;
    int pos;
};
 
// Comparator function which can compare
// the second element of structure used to
// sort pairs in increasing order of second value.
bool comparator(struct meeting m1, meeting m2)
{
    return (m1.end < m2.end);
}
 
// Function for finding maximum meeting in one room
void maxMeeting(int s[], int f[], int n)
{
    struct meeting meet[n];
    for (int i = 0; i < n; i++)
    {
        // Starting time of meeting i.
        meet[i].start = s[i];
         
        // Finishing time of meeting i
        meet[i].end = f[i];
         
        // Original position/index of meeting
        meet[i].pos = i + 1;
    }
 
    // Sorting of meeting according to their finish time.
    sort(meet, meet + n, comparator);
 
    // Vector for storing selected meeting.
    vector<int> m;
 
    // Initially select first meeting.
    m.push_back(meet[0].pos);
 
    // time_limit to check whether new
    // meeting can be conducted or not.
    int time_limit = meet[0].end;
 
    // Check for all meeting whether it
    // can be selected or not.
    for (int i = 1; i < n; i++) {
        if (meet[i].start >= time_limit)
        {
            // Push selected meeting to vector
            m.push_back(meet[i].pos);
             
            // Update time limit.
            time_limit = meet[i].end;
        }
    }
 
    // Print final selected meetings.
    for (int i = 0; i < m.size(); i++) {
        cout << m[i] << " ";
    }
}
 
// Driver code
int main()
{
    // Starting time
    int s[] = { 1, 3, 0, 5, 8, 5 };
     
    // Finish time
    int f[] = { 2, 4, 6, 7, 9, 9 };
     
    // Number of meetings.
    int n = sizeof(s) / sizeof(s[0]);
 
    // Function call
    maxMeeting(s, f, n);
 
    return 0;
}

Java

// Java program to find maximum number of meetings
import java.util.*;
 
// Comparator function which can compare
// the ending time of the meeting ans
// sort the list
class mycomparator implements Comparator<meeting>
{
    @Override
    public int compare(meeting o1, meeting o2)
    {
        if (o1.end < o2.end)
        {
             
            // Return -1 if second object is
            // bigger then first
            return -1;
        }
        else if (o1.end > o2.end)
         
            // Return 1 if second object is
            // smaller then first
            return 1;
             
        return 0;
    }
}
 
// Custom class for storing starting time, 
// finishing time and position of meeting.
class meeting
{
    int start;
    int end;
    int pos;
     
    meeting(int start, int end, int pos)
    {
        this.start = start;
        this.end = end;
        this.pos = pos;
    }
}
 
class GFG{
     
// Function for finding maximum meeting in one room
public static void maxMeeting(ArrayList<meeting> al, int s)
{
     
    // Initialising an arraylist for storing answer
    ArrayList<Integer> m = new ArrayList<>();
     
    int time_limit = 0;
     
    mycomparator mc = new mycomparator();
     
    // Sorting of meeting according to
    // their finish time.
    Collections.sort(al, mc);
     
    // Initially select first meeting.
    m.add(al.get(0).pos);
     
    // time_limit to check whether new 
    // meeting can be conducted or not.
    time_limit = al.get(0).end;
     
    // Check for all meeting whether it 
    // can be selected or not.
    for(int i = 1; i < al.size(); i++)
    {
        if (al.get(i).start > time_limit)
        {
             
            // Add selected meeting to arraylist
            m.add(al.get(i).pos);
             
            // Update time limit
            time_limit = al.get(i).end;
        }
    }
     
    // Print final selected meetings.
     for(int i = 0; i < m.size(); i++)
        System.out.print(m.get(i) + 1 + " ");
}
 
// Driver Code 
public static void main (String[] args)
{
     
    // Starting time
    int s[] = { 1, 3, 0, 5, 8, 5 };
     
    // Finish time
    int f[] = { 2, 4, 6, 7, 9, 9 }; 
     
    // Defining an arraylist of meet type
    ArrayList<meeting> meet = new ArrayList<>();
    for(int i = 0; i < s.length; i++)
     
        // Creating object of meeting
        // and adding in the list
        meet.add(new meeting(s[i], f[i], i));
         
    // Function call
    maxMeeting(meet, meet.size());
}
}
 
// This code is contributed by Sarthak Sethi

Python3

# Python3 program to find maximum number
# of meetings
 
# Custom class for storing starting time,
# finishing time and position of meeting.
class meeting:
     
    def __init__(self, start, end, pos):
         
        self.start = start
        self.end = end
        self.pos = pos
 
# Function for finding maximum
# meeting in one room
def maxMeeting(l, n):
 
    # Initialising an arraylist
    # for storing answer
    ans = []
     
    # Sorting of meeting according to
    # their finish time.
    l.sort(key = lambda x: x.end)
 
    # Initially select first meeting
    ans.append(l[0].pos)
 
    # time_limit to check whether new
    # meeting can be conducted or not.
    time_limit = l[0].end
     
    # Check for all meeting whether it
    # can be selected or not.
    for i in range(1, n):
        if l[i].start > time_limit:
            ans.append(l[i].pos)
            time_limit = l[i].end
             
    # Print final selected meetings
    for i in ans:
        print(i + 1, end = " ")
         
    print()
 
# Driver code
if __name__ == '__main__':
     
    # Starting time
    s = [ 1, 3, 0, 5, 8, 5 ]
 
    # Finish time
    f = [ 2, 4, 6, 7, 9, 9 ]
 
    # Number of meetings.
    n = len(s)
 
    l = []
 
    for i in range(n):
         
        # Creating object of meeting
        # and adding in the list
        l.append(meeting(s[i], f[i], i))
         
    # Function call
    maxMeeting(l, n)
 
# This code is contributed by MuskanKalra1

Output:

1 2 4 5

Time Complexity: O(N log(N))

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