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import java.util.Scanner;
public class Main {
public static void main(String[] args) {
int n ; //number of rows in the array / processes on the system
int m ; //the number of columns in array / different types of resources. Resource A, B, C, and D add up to 4
Scanner scanner = new Scanner(System.in);
System.out.print("Enter the number of processes present on the system: ");
n = scanner.nextInt();
System.out.print("Enter the number of different types of resources there are: ");
m = scanner.nextInt();
int[] total = new int[m]; //total resources present on the system
System.out.print("Enter the total amount of each resource present on the system (Order matters - type the number and press enter for each resource type): ");
for(int k = 0; k < m; k++){
total[k] = scanner.nextInt();
}
int[][] allocation = new int[n][m]; //resources currently allocated to the process
System.out.println("Enter the resources currently allocated to each process. Preserve the resource type order you entered previously: ");
for(int k1 = 0; k1 < n; k1++){ //for each process
System.out.println("Enter the resources allocated to process " + k1 + ":");
for(int k2 = 0; k2 < m; k2++){
allocation[k1][k2] = scanner.nextInt();
}
}
int[][] max = new int[n][m]; //maximum resources the process needs to complete execution
System.out.println("Enter the maximum resources each process needs. Preserve the resource type order you entered previously: ");
for(int k1 = 0; k1 < n; k1++){ //for each process
System.out.println("Enter the maximum resources needed by process " + k1 + ":");
for(int k2 = 0; k2 < m; k2++){
max[k1][k2] = scanner.nextInt();
}
}
System.out.println("Calculating available resources...");
int[] available = new int[m]; //total resources available after allocation
int[] totalAlloc = new int[m]; //all allocated resources added up - needed to calculate available
for(int k1 = 0; k1 < m; k1++){ //for each COLUMN
totalAlloc[k1] = 0; //initialize to zero first
for(int k2 = 0; k2 < n; k2++){
totalAlloc[k1] += allocation[k2][k1];
}
available[k1] = total[k1] - totalAlloc[k1]; //subtract the total allocated of a resource type from the total
}
//Calculating need matrix
System.out.println("Calculating need matrix...");
int[][] need = new int[n][m]; //resources that a process still needs in order to successfully execute
for(int i = 0; i < n; i++){
for(int j = 0; j < m; j++){
need[i][j] = max[i][j] - allocation[i][j];
}
}
System.out.println("Determining if the system is currently in a safe state...");
if(runSafetyAlgorithm(need, available, allocation, n, m)){
System.out.println("The system is in a safe state!");
}
else{
System.out.println("The system is in an UNSAFE state!");
}
//handling requests
boolean x = true;
boolean granted;
int input;
while(x){
System.out.println("Enter the process number of your request: ");
int reqNum = scanner.nextInt();
System.out.println("Enter the resources this process would like to request (preserve the order as previously): ");
for(int j = 0; j < m; j++){
input = scanner.nextInt();
allocation[reqNum][j] += input;
available[j] -= input;
}
//Re-Calculating need matrix
System.out.println("Calculating need matrix...");
for(int i = 0; i < n; i++){
for(int j = 0; j < m; j++){
need[i][j] = max[i][j] - allocation[i][j];
}
}
if(runSafetyAlgorithm(need, available, allocation, n, m)){
System.out.println("The system is in a safe state, so the request has been granted!");
}
else{
System.out.println("This request would leave the system in an unsafe state. The bank denies the request.");
}
System.out.println("Would you like to enter another request from this new state? (y/n): ");
String input2 = scanner.next();
if(input2.equals("y")){
//do nothing, go to beginning of while loop
}
else{
System.out.println("Exiting...");
x = false; //end the while loop and exit program
}
}
}
public static boolean runSafetyAlgorithm(int[][] need, int[] available, int [][] allocation, int n, int m){
//BEGINNING OF SAFETY ALGORITHM
//set work[][] = available[][] or unnecessary ?
boolean[] finish = new boolean[n]; //keeping track of whether a process has finished executing
//all processes have not finished at first - set all to false (using i instead of j here because we are dealing with columns)
for(int i = 0; i < n; i++){
finish[i] = false;
}
//while(!isFinished(finish)){ //while there is still a process that is not finished...
//I chose to repeat for the # of processes instead, because it is possible that a process will never finish (unsafe state in this case)
for(int i = 0; i < n; i++){
for(int i2 = 0; i2 < n; i2++){ //iterate through all processes (using i instead of j here because we are dealing with columns)
//if a process has not finished yet and its needs are less than what is available
if((finish[i2] == false) && (needLessThanAvailable(need[i2], available, m))){
for(int j = 0; j < m; j++){
available[j] += allocation[i2][j];
}
finish[i2] = true;
}
}
}
//determine if the system is in a safe state or not
boolean SafeState;
if(isFinished(finish)){
SafeState = true;
}
else{
SafeState = false;
}
return SafeState;
//END OF SAFETY ALGORITHM
}
//return true if all processes have finished executing
public static boolean isFinished(boolean[] finish){
for (boolean b : finish) {
if (b == false) {
return false;
}
}
return true;
}
//return true if the resource needs of a process are less than what is available
public static boolean needLessThanAvailable(int[] need, int [] available, int m){
for(int j = 0; j < m; j++){
if(need[j] > available[j]){
return false;
}
}
return true;
}
}
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