1 package 编程练习题chapter5; 2 import java.util.*; //我改了； 3 public class Exercise5_1 { 4 public static void main (String args[]) { 5 Scanner input = new Scanner(System.in); 6 7 System.out.print("Enter a number: "); 8 int number = input.nextInt(); 9 10 for (int i = 1; i <= number; i++) 11 getPentagonalNumber(i); 12 } 13 14 public static void getPentagonalNumber(int n){ 15 if (n % 10 == 0) 16 System.out.println(n * (3 * n - 1) / 2); 17 else 18 System.out.printf("%10d", n * (3 * n - 1) / 2); 19 20 } 21 }
package 编程练习题chapter5; public class Exercise5_2 { public static void main(String args[]){ java.util.Scanner input = new java.util.Scanner(System.in); System.out.print("Enter an interger: "); long value = input.nextInt(); System.out.println(sumDigits(value)); } public static int sumDigits(long n){ int temp = (int)Math.abs(n); int sum = 0; while (temp != 0) { int remainder = temp % 10; sum += remainder; temp = temp / 10; } return sum; } }
1 package 编程练习题chapter5; 2 //回文整数，例如234变成432，不一样不是回文数。252就是回文数。 3 public class Exercise5_3 { 4 public static void main (String args[]){ 5 java.util.Scanner input = new java.util.Scanner(System.in); 6 7 System.out.print("Enter a postive integer: "); 8 int number = input.nextInt(); 9 10 if (isPalindrome(number)) 11 System.out.println(number + " is palindrome"); 12 else 13 System.out.println(number + " is not palindrome"); 14 } 15 16 public static boolean isPalindrome(int number) { 17 return number == reverse(number); 18 } 19 20 public static int reverse(int number) { 21 int result = 0; 22 while (number != 0) { 23 int remainder = number % 10; 24 result = result * 10 + remainder; 25 number = number / 10; 26 } 27 return result; 28 } 29 }
1 package 编程练习题chapter5; 2 3 public class Exercise5_4 { 4 public static void main (String args[]){ 5 java.util.Scanner input = new java.util.Scanner(System.in); 6 7 System.out.print("Enter an integer: "); 8 int number = input.nextInt(); 9 reverse(number); 10 } 11 12 13 public static void reverse(int number) { 14 while (number != 0) { 15 int remainder = number % 10; 16 System.out.print(remainder); 17 number = number / 10; 18 } 19 20 System.out.println(); 21 } 22 }
1 package 编程练习题chapter5; 2 3 public class Exercise5_6 { 4 public static void main(String[] args){ 5 java.util.Scanner input = new java.util.Scanner(System.in); 6 System.out.print("Enter line number: "); 7 int lineNumber = input.nextInt(); 8 9 displayPattern(lineNumber); 10 } 11 12 public static void displayPattern(int n) { 13 for (int row = 1; row <= n; row++) { 14 15 for (int i = row; i < n; i++) 16 System.out.print(" "); 17 18 for (int i = row; i >= 1; i--) 19 System.out.print(" " + i); 20 21 System.out.println(); 22 23 } 24 } 25 }
1 package 编程练习题chapter5; //回文素数 2 3 public class Exercise5_26 { 4 public static void main(String args[]){ 5 int count = 1; 6 7 for (int i = 2; true; i++){ 8 if (isPrime(i) && isPalindrome(i)){ 9 System.out.print(i + " "); 10 11 if (count % 10 == 0){ 12 System.out.println(); 13 } 14 15 if (count == 100){ 16 break; 17 } 18 19 count++; 20 } 21 } 22 } 23 24 public static boolean isPrime(int num){ 25 if ((num == 1) || (num == 2)){ 26 return true; 27 } 28 29 for (int i = 2; i <= num / 2; i++){ 30 if (num % i == 0){ 31 return false; 32 } 33 } 34 35 return true; 36 } 37 38 static int reversal(int num){ 39 int result = 0; 40 41 while (num != 0){ 42 int lastDigit = num % 10; 43 result = result * 10 + lastDigit; 44 num = num / 10; 45 } 46 47 return result; 48 } 49 50 static boolean isPalindrome(int num){ 51 return num == reversal(num); 52 } 53 54 }
1 package 编程练习题chapter5; 2 3 public class Exercise5_33 { 4 public static void main (String args[]){ 5 long seconds = System.currentTimeMillis() / 1000; 6 long currentSecond = seconds % 60; 7 long minutes = seconds / 60; 8 long currentMinute = minutes % 60; 9 long hours = minutes / 60; 10 long currentHour = hours % 24; 11 long days = hours / 24 + 1; 12 13 int year = 1970; //get year; 14 while (days >= (isLeapYear(year) ? 366 : 365)) { 15 days = days - (isLeapYear(year) ? 366 : 365); 16 year++; 17 } 18 19 int month = 1; //get month; 20 while (days >= getNumberOfDaysInMonth(year, month)) { 21 days = days - getNumberOfDaysInMonth(year, month); 22 month++; 23 } 24 25 System.out.println("Current data and time is " + 26 getMonthName(month) + " " + days + "," + year + " " + 27 currentHour + ":" + currentMinute + ":" + currentSecond); 28 } 29 30 public static String getMonthName(int month) { 31 String monthName = null; 32 switch (month) { 33 case 1: monthName = "January"; break; 34 case 2: monthName = "February"; break; 35 case 3: monthName = "March"; break; 36 case 4: monthName = "April"; break; 37 case 5: monthName = "May"; break; 38 case 6: monthName = "June"; break; 39 case 7: monthName = "July"; break; 40 case 8: monthName = "August"; break; 41 case 9: monthName = "September"; break; 42 case 10: monthName = "October"; break; 43 case 11: monthName = "November"; break; 44 case 12: monthName = "December"; 45 } 46 47 return monthName; 48 } 49 50 public static int getNumberOfDaysInMonth(int year, int month) { 51 if (month == 1 || month == 3 || month == 5 || month == 7 || 52 month == 8 || month == 10 || month == 12) 53 return 31; 54 55 if (month == 4 || month == 6 || month == 9 || month == 11) 56 return 30; 57 58 if (month == 2) return isLeapYear(year) ? 29 : 28; 59 60 return 0; 61 } 62 63 public static boolean isLeapYear(int year) { 64 return year % 400 == 0 || (year % 4 == 0 && year % 100 != 0); 65 } 66 }