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java-analysis-tester/foo2.java at master · GithubMericoTestingDb/java-analysis-tester · GitHub
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import
java
.
math
.
BigInteger
;
import
java
.
util
.
Random
;
public
class
PrimeEx
{
/**
* @param args
*/
public
static
void
main
(
String
[]
args
) {
printTest
(
10
,
4
);
printTest
(
2
,
2
);
printTest
(
54161329
,
4
);
printTest
(
1882341361
,
2
);
printTest
(
36
,
9
);
System
.
out
.
println
(
isPrime
(
54161329
) +
" expect false"
);
System
.
out
.
println
(
isPrime
(
1882341361
) +
" expect true"
);
System
.
out
.
println
(
isPrime
(
2
) +
" expect true"
);
int
numPrimes
=
0
;
Stopwatch
s
=
new
Stopwatch
();
s
.
start
();
for
(
int
i
=
2
;
i
<
10000000
;
i
++) {
if
(
isPrime
(
i
)) {
numPrimes
++;
}
}
s
.
stop
();
System
.
out
.
println
(
numPrimes
+
" "
+
s
);
s
.
start
();
boolean
[]
primes
=
getPrimes
(
10000000
);
int
np
=
0
;
for
(
boolean
b
:
primes
)
if
(
b
)
np
++;
s
.
stop
();
System
.
out
.
println
(
np
+
" "
+
s
);
System
.
out
.
println
(
new
BigInteger
(
1024
,
10
,
new
Random
()));
}
public
static
boolean
[]
getPrimes
(
int
max
) {
boolean
[]
result
=
new
boolean
[
max
+
1
];
for
(
int
i
=
2
;
i
<
result
.
length
;
i
++)
result
[
i
] =
true
;
final
double
LIMIT
=
Math
.
sqrt
(
max
);
for
(
int
i
=
2
;
i
<=
LIMIT
;
i
++) {
if
(
result
[
i
]) {
// cross out all multiples;
int
index
=
2
*
i
;
while
(
index
<
result
.
length
){
result
[
index
] =
false
;
index
+=
i
;
}
}
}
return
result
;
}
public
static
void
printTest
(
int
num
,
int
expectedFactors
) {
Stopwatch
st
=
new
Stopwatch
();
st
.
start
();
int
actualFactors
=
numFactors
(
num
);
st
.
stop
();
System
.
out
.
println
(
"Testing "
+
num
+
" expect "
+
expectedFactors
+
", "
+
"actual "
+
actualFactors
);
if
(
actualFactors
==
expectedFactors
)
System
.
out
.
println
(
"PASSED"
);
else
System
.
out
.
println
(
"FAILED"
);
System
.
out
.
println
(
st
.
time
());
}
// pre: num >= 2
public
static
boolean
isPrime
(
int
num
) {
assert
num
>=
2
:
"failed precondition. num must be >= 2. num: "
+
num
;
final
double
LIMIT
=
Math
.
sqrt
(
num
);
boolean
isPrime
= (
num
==
2
) ?
true
:
num
%
2
!=
0
;
int
div
=
3
;
while
(
div
<=
LIMIT
&&
isPrime
) {
isPrime
=
num
%
div
!=
0
;
div
+=
2
;
}
return
isPrime
;
}
// pre: num >= 2
public
static
int
numFactors
(
int
num
) {
assert
num
>=
2
:
"failed precondition. num must be >= 2. num: "
+
num
;
int
result
=
0
;
final
double
SQRT
=
Math
.
sqrt
(
num
);
for
(
int
i
=
1
;
i
<
SQRT
;
i
++) {
if
(
num
%
i
==
0
) {
result
+=
2
;
}
}
if
(
num
%
SQRT
==
0
)
result
++;
return
result
;
}
}
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