Java Reference
In-Depth Information
Your program should display
The tickets don't cover all numbers
How do you mark a number as covered? You can create an array with
99 boolean
elements.
Each element in the array can be used to mark whether a number is covered. Let the array be
isCovered
. Initially, each element is
false
, as shown in Figure 6.2a. Whenever a number is
read, its corresponding element is set to
true
. Suppose the numbers entered are
1
,
2
,
3
,
99
,
0
. When number
1
is read,
isCovered[0]
is set to
true
(see Figure 6.2b). When
number
2
is read,
isCovered[2 - 1]
is set to
true
(see Figure 6.2c). When number
3
is read,
isCovered[3 - 1]
is set to
true
(see Figure 6.2d). When number
99
is read,
isCovered[98]
is set to
true
(see Figure 6.2e).
isCovered
isCovered
isCovered
isCovered
isCovered
[0]
[1]
[2]
[3]
false
false
false
false
.
.
.
false
false
[0]
[1]
[2]
[3]
true
[0]
[1]
[2]
[3]
true
[0]
[1]
[2]
[3]
true
[0]
[1]
[2]
[3]
true
true
true
false
false
false
.
.
.
false
false
true
true
false
false
.
.
.
false
false
true
false
.
.
.
false
false
false
.
.
.
false
[97]
[98]
[97]
[98]
[97]
[98]
[97]
[98]
[97]
[98]
true
(a)
(b)
(c)
(d)
(e)
F
IGURE
6.2
If number
i
appears in a Lotto ticket,
isCovered[i-1]
is set to
true
.
The algorithm for the program can be described as follows:
for each number k read from the file,
mark number k as covered by setting isCovered[k - 1] true;
if every isCovered[i] is true
The tickets cover all numbers
else
The tickets don't cover all numbers
The complete program is given in Listing 6.1.
L
ISTING
6.1
LottoNumbers.java
1
import
java.util.Scanner;
2
3
public class
LottoNumbers {
4
public static void
main(String[] args) {
5 Scanner input =
new
Scanner(System.in);
6
boolean
[] isCovered =
new boolean
[
99
];
// Default is false
create and initialize array
7
8
// Read each number and mark its corresponding element covered
9
int
number = input.nextInt();
10
while
(number !=
0
) {
11 isCovered[number -
1
] =
true
;
12 number = input.nextInt();
13 }
14
read number
mark number covered
read number
