DeadCodeElimination.java

import java.util.*;

public class CODeadCodeElimination {
    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the number of expressions:");
        int n = sc.nextInt();
    	
    	sc.nextLine();
    	System.out.println("Enter the expression: ");
    	String prog[] = new String[100];
    	for(int i = 0; i < n; i++) {
		  prog[i] = sc.nextLine();
	}
        sc.close();

        int k = 0, l = 0;
        String newProg[] = new String[100];
        String variables[] = new String[100];
        for(int i = 0; i < n; i++) {
        	if(prog[i].contains("=")) {
        		String tokens[] = prog[i].split("=");
            		String variable = tokens[0].trim();
            		boolean isUsed = false;

            		//Check if variable is used in the rest of the program
	  		for(int j = i+1; j < n; j++) {
			    if(prog[j].contains(variable)) {
				variables[l++] = tokens[0].trim();
			    }
	  		}
			 if(Arrays.asList(variables).contains(variable)) {
			    //Variable was used earlier
			    isUsed = true;
			 }
			 if(isUsed) {
			    //Only add the variables that are used later
			    newProg[k++] = prog[i];
			 }
		}	

        }
        
	System.out.println("\nAfter performing Dead Code Elimination:");
    	for(int i = 0; i < k; i++) {
		System.out.println(newProg[i]);
	}
    }
}

/*

OUTPUT:

Enter the number of expressions:
4
Enter the expression:
a=2;
b=3;
c=4;
a=a+2;

After performing Dead Code Elimination:
a=2;
a=a+2;

*/