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Make the intervals non-overlapping by assigning them to two different processors

Last Updated : 17 Mar, 2023
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Given a list of intervals interval[] where each interval contains two integers L and R, the task is to assign intervals to two different processors such that there are no overlapping intervals for each processor. To assign the interval[i] to the first processor, print “F” and to assign it to the second processor, print “S”.
Note: If there is no possible solution print -1.
Examples: 

Input: interval[] = {{360, 480}, {420, 540}, {600, 660}} 
Output: S, F, S 
Explanation: 
The intervals assigned to processors are – 
Intervals of First Processor {{420, 540}} 
Intervals of Second Processor {{360, 480}, {600, 660}} 
As there are no overlapping intervals for each processor, it will be a valid solution.

Input: interval[] = {{99, 150}, {1, 100}, {100, 301}, {2, 5}, {150, 250}} 
Output: S, F, F, S, S 
Explanation: 
The intervals assigned to processors are – 
Intervals of First Processor {{1, 100}, {100, 301}} 
Intervals of Second Processor {{99, 150}, {2, 5}, {150, 250}} 
As there are no overlapping intervals for each processor, it will be a valid solution. 

Approach: The idea is to use Greedy algorithm to assign the intervals to the processor. 
If the highest end time of the processor is less than or equal to start time of an interval, then this interval can be assigned to the processor. Otherwise, check for the another processor. If any interval cannot be assigned to any processor then there is no possible solution. 
Below is the illustration of the steps of the approach: 

  • As in the current problem we have to print according to the order of the intervals. So to save the order of intervals, pair the intervals with their index.
  • Sort the intervals by their start time. i.e. L.
  • Iterate over the intervals and assign the intervals to the processors as follows:  
if (interval[i][0] >= firstProcessorEndTime)
    answer[interval[i]] = "F"
    firstProcessorEndTime = 
        max(firstProcessorEndTime, interval[i][0])
else if (interval[i][0] >= secondProcessorEndTime)
    answer[interval[i]] = "S"
    secondProcessorEndTime = 
        max(secondProcessorEndTime, interval[i][0])
else
    print(-1)

Below is the implementation of the above approach:

C++




// C++ implementation for intervals
// scheduling to two processors such
// that there are no overlapping intervals
#include <bits/stdc++.h>
using namespace std;
 
// Function to assign the intervals
// to two different processors
void assignIntervals(vector<vector<int> > interval, int n)
{
 
    //  Loop to pair the interval
    //  with their indices
    for (int i = 0; i < n; i++)
        interval[i].push_back(i);
 
    // sorting the interval by
    // their start times
    sort(interval.begin(), interval.end());
 
    int firstEndTime = -1;
    int secondEndTime = -1;
    char find = ' ';
    bool flag = false;
 
    // Loop to iterate over the
    // intervals with their start time
    for (int i = 0; i < n; i++) {
        if (interval[i][0] >= firstEndTime) {
            firstEndTime = interval[i][1];
            interval[i].push_back('S');
        }
        else if (interval[i][0] >= secondEndTime) {
            secondEndTime = interval[i][1];
            interval[i].push_back('F');
        }
        else {
            flag = true;
            break;
        }
    }
 
    // Condition to check if there
    // is a possible solution
    if (flag)
        cout << (-1);
    else {
        vector<char> form(n, ' ');
 
        for (int i = 0; i < n; i++) {
            int indi = interval[i][2];
            form[indi] = interval[i][3];
        }
 
        // form = ''.join(form)
        for (int i = 0; i < form.size(); i++)
            cout << form[i] << ",";
    }
}
 
// Driver Code
int main()
{
 
    vector<vector<int> > intervals
        = { { 360, 480 }, { 420, 540 }, { 600, 660 } };
 
    // Function Call
    assignIntervals(intervals, intervals.size());
    return 0;
}


Java




// Java program for the above approach
import java.util.*;
 
public class Main {
 
    public static void main(String[] args) {
        // Intervals to be scheduled
        int[][] intervals = {
            { 360, 480 },
            { 420, 540 },
            { 600, 660 }
        };
 
        // Function Call
        assignIntervals(intervals, intervals.length);
    }
 
    // Function to assign the intervals
    // to two different processors
    public static void assignIntervals(int[][] interval, int n) {
 
        // Loop to pair the interval
        // with their indices
        for (int i = 0; i < n; i++) {
            interval[i] = Arrays.copyOf(interval[i], interval[i].length + 1);
            interval[i][interval[i].length - 1] = i;
        }
 
        // Sorting the interval by their start times
        Arrays.sort(interval, Comparator.comparingInt(a -> a[0]));
 
        int firstEndTime = -1;
        int secondEndTime = -1;
        boolean flag = false;
 
        // Loop to iterate over the
        // intervals with their start time
        for (int i = 0; i < n; i++) {
            if (interval[i][0] >= firstEndTime) {
                firstEndTime = interval[i][1];
                interval[i] = Arrays.copyOf(interval[i], interval[i].length + 1);
                interval[i][interval[i].length - 1] = 'S';
            } else if (interval[i][0] >= secondEndTime) {
                secondEndTime = interval[i][1];
                interval[i] = Arrays.copyOf(interval[i], interval[i].length + 1);
                interval[i][interval[i].length - 1] = 'F';
            } else {
                flag = true;
                break;
            }
        }
 
        // Condition to check if there
        // is a possible solution
        if (flag) {
            System.out.println("-1");
        } else {
            List<Character> form = new ArrayList<>(Collections.nCopies(n, ' '));
            for (int i = 0; i < n; i++) {
                int indi = interval[i][2];
                form.set(indi, (char) interval[i][3]);
            }
 
            // Print the result
            String output = form.toString();
            System.out.println(output);
        }
    }
}
 
// This code is contributed by Prince Kumar


Python3




# Python implementation for intervals
# scheduling to two processors such
# that there are no overlapping intervals
 
# Function to assign the intervals
# to two different processors
def assignIntervals(interval, n):
     
    # Loop to pair the interval
    # with their indices
    for i in range(n):
        interval[i].append(i)
         
    # sorting the interval by
    # their startb times
    interval.sort(key = lambda x: x[0])
     
    firstEndTime = -1
    secondEndTime = -1
    find = ''
    flag = False
     
    # Loop to iterate over the
    # intervals with their start time
    for i in range(n):
        if interval[i][0] >= firstEndTime:
            firstEndTime = interval[i][1]
            interval[i].append('S')
        elif interval[i][0] >= secondEndTime:
            secondEndTime = interval[i][1]
            interval[i].append('F')
        else:
            flag = True
            break
     
    # Condition to check if there
    # is a possible solution
    if flag:
        print(-1)
    else:
        form = ['']*n
        for i in range(n):
            indi = interval[i][2]
            form[indi] = interval[i][3]
        # form = ''.join(form)
        print(form, ", ")
 
# Driver Code   
if __name__ == "__main__":
    intervals = [[360, 480], [420, 540], [600, 660]]
     
    # Function Call
    assignIntervals(intervals, len(intervals))


C#




using System;
using System.Collections.Generic;
using System.Linq;
 
class MainClass {
    public static void Main(string[] args) {
        // intervals to be scheduled
        int[][] intervals = {
            new int[] {360, 480},
            new int[] {420, 540},
            new int[] {600, 660}
        };
 
        // Function Call
        AssignIntervals(intervals, intervals.Length);
    }
 
    // Function to assign the intervals
    // to two different processors
    public static void AssignIntervals(int[][] interval, int n) {
        //  Loop to pair the interval
        //  with their indices
        for (int i = 0; i < n; i++) {
            interval[i] = interval[i].Concat(new int[] {i}).ToArray();
        }
 
        // sorting the interval by
        // their start times
        interval = interval.OrderBy(x => x[0]).ToArray();
 
        int firstEndTime = -1;
        int secondEndTime = -1;
        bool flag = false;
 
        // Loop to iterate over the
        // intervals with their start time
        for (int i = 0; i < n; i++) {
            if (interval[i][0] >= firstEndTime) {
                firstEndTime = interval[i][1];
                interval[i] = interval[i].Concat(new int[] {'S'}).ToArray();
            } else if (interval[i][0] >= secondEndTime) {
                secondEndTime = interval[i][1];
                interval[i] = interval[i].Concat(new int[] {'F'}).ToArray();
            } else {
                flag = true;
                break;
            }
        }
 
        // Condition to check if there
        // is a possible solution
        if (flag) {
            Console.WriteLine("-1");
        } else {
            List<char> form = new List<char>(new char[n]);
 
            for (int i = 0; i < n; i++) {
                int indi = interval[i][2];
                form[indi] = (char)interval[i][3];
            }
 
            string output = string.Join( ",", form);
 
            Console.WriteLine("["+output+"]");
        }
    }
}


Javascript




// JavaScript implementation for intervals
// scheduling to two processors such
// that there are no overlapping intervals
 
// Function to assign the intervals
// to two different processors
function assignIntervals(interval, n) {
     
    // Loop to pair the interval
    // with their indices
    for (let i = 0; i < n; i++) {
        interval[i].push(i);
    }
     
    // sorting the interval by
    // their startb times
    interval.sort((a, b) => a[0] - b[0]);
     
    let firstEndTime = -1;
    let secondEndTime = -1;
    let find = '';
    let flag = false;
     
    // Loop to iterate over the
    // intervals with their start time
    for (let i = 0; i < n; i++) {
        if (interval[i][0] >= firstEndTime) {
            firstEndTime = interval[i][1];
            interval[i].push('S');
        } else if (interval[i][0] >= secondEndTime) {
            secondEndTime = interval[i][1];
            interval[i].push('F');
        } else {
            flag = true;
            break;
        }
    }
     
    // Condition to check if there
    // is a possible solution
    if (flag) {
        console.log(-1);
    } else {
        let form = Array(n).fill('');
        for (let i = 0; i < n; i++) {
            let indi = interval[i][2];
            form[indi] = interval[i][3];
        }
        // form = form.join('');
        console.log(form, ", ");
    }
}
 
// Driver Code
let intervals = [[360, 480], [420, 540], [600, 660]];
 
// Function Call
assignIntervals(intervals, intervals.length);
 
// This code is contributed by phasing17.


Output

S,F,S,

Time Complexity: O(NlogN)
Auxiliary Space: O(N) 



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