问题
I want to link and sort in descending order a two dimensional array. I coded my program in a way so that you can print the array but it is not sorted. How can I make it sorted?
This is a program to calculate the number of hours worked by 8 employees during the week (7 days), and print them out in descending order:
public class WeeklyHours {
public static void main(String[] args) {
double[][] employeeWorkHours = {
{ 2, 4, 3, 4, 5, 8, 8 },
{ 7, 3, 4, 3, 3, 4, 4 },
{ 3, 3, 4, 3, 3, 2, 2 },
{ 9, 3, 4, 7, 3, 4, 1 },
{ 3, 5, 4, 3, 6, 3, 8 },
{ 3, 4, 4, 6, 3, 4, 4 },
{ 3, 7, 4, 8, 3, 8, 4 },
{ 6, 3, 5, 9, 2, 7, 9 } };
for (int row = 0; row < employeeWorkHours.length; row++)
System.out.println("Employee " + row + " : "
+ sumRow(employeeWorkHours, row));
}
public static double sumRow(double[][] m, int rowIndex) {
double total = 0;
for (int col = 0; col < m[0].length; col++) {
total += m[rowIndex][col];
}
return total;
}
}
This is what I got in the console:
Employee 0 : 34.0
Employee 1 : 28.0
Employee 2 : 20.0
Employee 3 : 31.0
Employee 4 : 32.0
Employee 5 : 28.0
Employee 6 : 37.0
Employee 7 : 41.0
But I am supposed to get something like this:
Employee 7: 41
Employee 6: 37
Employee 0: 34
Employee 4: 32
Employee 3: 31
Employee 1: 28
Employee 5: 28
Employee 2: 20
回答1:
Try the Arrays.sort() method that takes a custom Comparator (source: this answer):
java.util.Arrays.sort(employeeWorkHours, new java.util.Comparator<double[]>() {
public int compare(double[] a, double[] b) {
return Double.compare(a[0], b[0]);
}
});
If you don't feel like using the Java API, here's selection sort on a two-dimensional array:
int numEmployees = employeeWorkHours.length; // for convenience
// Looping through each of the employees
for(int employee = 0; employee < numEmployees; employee++) {
// Find the employee who's worked the most out of the remaining ones
int maxTimeEmployee = employee; // Start with the current one
for(int i = employee; i < numEmployees; i++) {
if(sumRow(employeeWorkHours, i) > sumRow(employeeWorkHours, maxTimeEmployee)) {
// We've found a new maximum
maxTimeEmployee = i;
}
}
// Swap the current employee with the maximum one
double[] tempHours = employeeWorkHours[employee];
employeeWorkHours[employee] = employeeWorkHours[maxTimeEmployee];
employeeWorkHours[maxTimeEmployee] = tempHours;
}
回答2:
I suggest you start with an Employee POJO to store the weekly hours and employee number like
static class Employee implements Comparable<Employee> {
int num;
double hours;
public Employee(int num, double hours) {
this.num = num;
this.hours = hours;
}
public int getNum() {
return num;
}
public void setNum(int num) {
this.num = num;
}
public double getHours() {
return hours;
}
public void setHours(double hours) {
this.hours = hours;
}
@Override
public String toString() {
return String.format("Employee #%d - Hours %.1f", num, hours);
}
@Override
public int compareTo(Employee o) {
int c = Double.valueOf(this.hours).compareTo(o.hours);
if (c != 0) {
return -c;
}
return Integer.valueOf(this.num).compareTo(o.num);
}
}
Then you can implement your sumRow with a for-each and something like
public static double sumRow(double[] m) {
double total = 0;
for (double val : m) {
total += val;
}
return total;
}
And finally, I think your main() could then use Arrays.sort(Object[]) like
public static void main(String[] args) {
double[][] employeeWorkHours = { { 2, 4, 3, 4, 5, 8, 8 },
{ 7, 3, 4, 3, 3, 4, 4 }, { 3, 3, 4, 3, 3, 2, 2 },
{ 9, 3, 4, 7, 3, 4, 1 }, { 3, 5, 4, 3, 6, 3, 8 },
{ 3, 4, 4, 6, 3, 4, 4 }, { 3, 7, 4, 8, 3, 8, 4 },
{ 6, 3, 5, 9, 2, 7, 9 } };
Employee[] totals = new Employee[employeeWorkHours.length];
for (int i = 0; i < employeeWorkHours.length; i++) {
totals[i] = new Employee(i, sumRow(employeeWorkHours[i]));
}
Arrays.sort(totals);
for (Employee e : totals) {
System.out.println(e);
}
}
And I get what I think is the correct output,
Employee #7 - Hours 41.0
Employee #6 - Hours 37.0
Employee #0 - Hours 34.0
Employee #4 - Hours 32.0
Employee #3 - Hours 31.0
Employee #1 - Hours 28.0
Employee #5 - Hours 28.0
Employee #2 - Hours 20.0
回答3:
With a few changes to your code:
public class WeeklyHours {
public static void main(String[] args) {
double[][] employeeWorkHours = {
{ 2, 4, 3, 4, 5, 8, 8 },
{ 7, 3, 4, 3, 3, 4, 4 },
{ 3, 3, 4, 3, 3, 2, 2 },
{ 9, 3, 4, 7, 3, 4, 1 },
{ 3, 5, 4, 3, 6, 3, 8 },
{ 3, 4, 4, 6, 3, 4, 4 },
{ 3, 7, 4, 8, 3, 8, 4 },
{ 6, 3, 5, 9, 2, 7, 9 } };
int len=employeeWorkHours.length;
double[][] employeeTotal=new double [len][2];
for (int row = 0; row < len; row++) {
employeeTotal[row][0]=row;
employeeTotal[row][1]=sumRow(employeeWorkHours, row);
System.out.println("Employee " + (int)employeeTotal[row][0] +
" : " + employeeTotal[row][1]);
}
System.out.println("\nOrder by Hours:");
Arrays.sort(employeeTotal, new java.util.Comparator<double[]>() {
public int compare(double[] a, double[] b) {
return Double.compare(b[1], a[1]);
}
});
for (int row = 0; row < len; row++)
System.out.println("Employee " + (int) employeeTotal[row][0] +
" : " + employeeTotal[row][1]);
}
public static double sumRow(double[][] m, int rowIndex) {
double total = 0;
for (int col = 0; col < m[0].length; col++) {
total += m[rowIndex][col];
}
return total;
}
来源：https://stackoverflow.com/questions/26748842/how-to-display-in-descending-order-a-two-dimensional-array