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Java/Dynamic Programming/Fibonacci.java at master · Germanus/Java · GitHub
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import
java
.
io
.
BufferedReader
;
import
java
.
io
.
InputStreamReader
;
import
java
.
util
.
HashMap
;
import
java
.
util
.
Map
;
/**
* @author Varun Upadhyay (https://github.com/varunu28)
* @author yanglbme (https://github.com/yanglbme)
*/
public
class
Fibonacci
{
private
static
Map
<
Integer
,
Integer
>
map
=
new
HashMap
<>();
public
static
void
main
(
String
[]
args
)
throws
Exception
{
BufferedReader
br
=
new
BufferedReader
(
new
InputStreamReader
(
System
.
in
));
int
n
=
Integer
.
parseInt
(
br
.
readLine
());
// Methods all returning [0, 1, 1, 2, 3, 5, ...] for n = [0, 1, 2, 3, 4, 5, ...]
System
.
out
.
println
(
fibMemo
(
n
));
System
.
out
.
println
(
fibBotUp
(
n
));
}
/**
* This method finds the nth fibonacci number using memoization technique
*
* @param n The input n for which we have to determine the fibonacci number
* Outputs the nth fibonacci number
**/
private
static
int
fibMemo
(
int
n
) {
if
(
map
.
containsKey
(
n
)) {
return
map
.
get
(
n
);
}
int
f
;
if
(
n
<=
1
) {
f
=
n
;
}
else
{
f
=
fibMemo
(
n
-
1
) +
fibMemo
(
n
-
2
);
map
.
put
(
n
,
f
);
}
return
f
;
}
/**
* This method finds the nth fibonacci number using bottom up
*
* @param n The input n for which we have to determine the fibonacci number
* Outputs the nth fibonacci number
**/
private
static
int
fibBotUp
(
int
n
) {
Map
<
Integer
,
Integer
>
fib
=
new
HashMap
<>();
for
(
int
i
=
0
;
i
<=
n
;
i
++) {
int
f
;
if
(
i
<=
1
) {
f
=
i
;
}
else
{
f
=
fib
.
get
(
i
-
1
) +
fib
.
get
(
i
-
2
);
}
fib
.
put
(
i
,
f
);
}
return
fib
.
get
(
n
);
}
/**
* This method finds the nth fibonacci number using bottom up
*
* @param n The input n for which we have to determine the fibonacci number
* Outputs the nth fibonacci number
* <p>
* This is optimized version of Fibonacci Program. Without using Hashmap and recursion.
* It saves both memory and time.
* Space Complexity will be O(1)
* Time Complexity will be O(n)
* <p>
* Whereas , the above functions will take O(n) Space.
* @author Shoaib Rayeen (https://github.com/shoaibrayeen)
**/
private
static
int
fibOptimized
(
int
n
) {
if
(
n
==
0
) {
return
0
;
}
int
prev
=
0
,
res
=
1
,
next
;
for
(
int
i
=
2
;
i
<
n
;
i
++) {
next
=
prev
+
res
;
prev
=
res
;
res
=
next
;
}
return
res
;
}
}
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