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JavaArithmetic/src/LeetCode/LeetCode279_no.java at master · git-jhy/JavaArithmetic · GitHub
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LeetCode
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LeetCode279_no.java
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JavaArithmetic
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src
/
LeetCode
/
LeetCode279_no.java
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package
LeetCode
;
import
javafx
.
util
.
Pair
;
import
java
.
util
.
LinkedList
;
public
class
LeetCode279_no
{
// 279. Perfect Squares
// https://leetcode.com/problems/perfect-squares/description/
// 该方法会导致 Time Limit Exceeded 或者 Memory Limit Exceeded
//
// 时间复杂度: O(2^n)
// 空间复杂度: O(2^n)
public
int
numSquares
(
int
n
) {
LinkedList
<
Pair
<
Integer
,
Integer
>>
queue
=
new
LinkedList
<
Pair
<
Integer
,
Integer
>>();
queue
.
addLast
(
new
Pair
<
Integer
,
Integer
>(
n
,
0
));
while
(!
queue
.
isEmpty
()) {
Pair
<
Integer
,
Integer
>
front
=
queue
.
removeFirst
();
int
num
=
front
.
getKey
();
int
step
=
front
.
getValue
();
if
(
num
==
0
)
return
step
;
for
(
int
i
=
1
;
num
-
i
*
i
>=
0
;
i
++)
queue
.
addLast
(
new
Pair
(
num
-
i
*
i
,
step
+
1
));
}
throw
new
IllegalStateException
(
"No Solution."
);
}
// 使用visited数组,记录每一个入队元素
// 时间复杂度: O(n)
// 空间复杂度: O(n)
public
int
numSquares2
(
int
n
) {
LinkedList
<
Pair
<
Integer
,
Integer
>>
queue
=
new
LinkedList
<
Pair
<
Integer
,
Integer
>>();
queue
.
addLast
(
new
Pair
<
Integer
,
Integer
>(
n
,
0
));
boolean
[]
visited
=
new
boolean
[
n
+
1
];
visited
[
n
] =
true
;
while
(!
queue
.
isEmpty
()) {
Pair
<
Integer
,
Integer
>
front
=
queue
.
removeFirst
();
int
num
=
front
.
getKey
();
int
step
=
front
.
getValue
();
if
(
num
==
0
)
return
step
;
for
(
int
i
=
1
;
num
-
i
*
i
>=
0
;
i
++)
if
(!
visited
[
num
-
i
*
i
]) {
queue
.
addLast
(
new
Pair
(
num
-
i
*
i
,
step
+
1
));
visited
[
num
-
i
*
i
] =
true
;
}
}
throw
new
IllegalStateException
(
"No Solution."
);
}
// 时间复杂度: O(n)
// 空间复杂度: O(n)
public
int
numSquares3
(
int
n
) {
if
(
n
==
0
)
return
0
;
LinkedList
<
Pair
<
Integer
,
Integer
>>
queue
=
new
LinkedList
<
Pair
<
Integer
,
Integer
>>();
queue
.
addLast
(
new
Pair
<
Integer
,
Integer
>(
n
,
0
));
boolean
[]
visited
=
new
boolean
[
n
+
1
];
visited
[
n
] =
true
;
while
(!
queue
.
isEmpty
()) {
Pair
<
Integer
,
Integer
>
front
=
queue
.
removeFirst
();
int
num
=
front
.
getKey
();
int
step
=
front
.
getValue
();
if
(
num
==
0
)
return
step
;
for
(
int
i
=
1
;
num
-
i
*
i
>=
0
;
i
++) {
int
a
=
num
-
i
*
i
;
if
(!
visited
[
a
]) {
if
(
a
==
0
)
return
step
+
1
;
queue
.
addLast
(
new
Pair
(
num
-
i
*
i
,
step
+
1
));
visited
[
num
-
i
*
i
] =
true
;
}
}
}
throw
new
IllegalStateException
(
"No Solution."
);
}
public
static
void
main
(
String
[]
args
) {
System
.
out
.
println
((
new
LeetCode279_no
()).
numSquares
(
12
));
System
.
out
.
println
((
new
LeetCode279_no
()).
numSquares
(
13
));
}
}
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