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Java Program for Activity Selection Problem | Greedy Algo-1
  • Difficulty Level : Basic
  • Last Updated : 22 Aug, 2019

You are given n activities with their start and finish times. Select the maximum number of activities that can be performed by a single person, assuming that a person can only work on a single activity at a time.
Example:

Example 1 : Consider the following 3 activities sorted
by finish time.
     start[]  =  {10, 12, 20};
     finish[] =  {20, 25, 30};
A person can perform at most two activities. The 
maximum set of activities that can be executed 
is {0, 2} [ These are indexes in start[] and 
finish[] ]

Example 2 : Consider the following 6 activities 
sorted by by finish time.
     start[]  =  {1, 3, 0, 5, 8, 5};
     finish[] =  {2, 4, 6, 7, 9, 9};
A person can perform at most four activities. The 
maximum set of activities that can be executed 
is {0, 1, 3, 4} [ These are indexes in start[] and 
finish[] ]

Java

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// The following implementation assumes that the activities
// are already sorted according to their finish time
import java.util.*;
import java.lang.*;
import java.io.*;
  
class ActivitySelection {
    // Prints a maximum set of activities that can be done by a single
    // person, one at a time.
    // n   -->  Total number of activities
    // s[] -->  An array that contains start time of all activities
    // f[] -->  An array that contains finish time of all activities
    public static void printMaxActivities(int s[], int f[], int n)
    {
        int i, j;
  
        System.out.print("Following activities are selected : n");
  
        // The first activity always gets selected
        i = 0;
        System.out.print(i + " ");
  
        // Consider rest of the activities
        for (j = 1; j < n; j++) {
            // If this activity has start time greater than or
            // equal to the finish time of previously selected
            // activity, then select it
            if (s[j] >= f[i]) {
                System.out.print(j + " ");
                i = j;
            }
        }
    }
  
    // driver program to test above function
    public static void main(String[] args)
    {
        int s[] = { 1, 3, 0, 5, 8, 5 };
        int f[] = { 2, 4, 6, 7, 9, 9 };
        int n = s.length;
  
        printMaxActivities(s, f, n);
    }
}

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Output:

Following activities are selected : n0 1 3 4

Please refer complete article on Activity Selection Problem | Greedy Algo-1 for more details!




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