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pygorithm/pygorithm/data_structures/stack.py at master · mikechen66/pygorithm · GitHub
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stack.py
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data_structures
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stack.py
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"""
Author: OMKAR PATHAK
Created On: 3rd August 2017
"""
from
string
import
ascii_letters
import
inspect
class
Stack
(
object
):
"""
Stack object
"""
def
__init__
(
self
,
limit
=
10
):
"""
:param limit: the stack size
"""
self
.
stack
=
[]
self
.
limit
=
limit
def
__str__
(
self
):
return
' '
.
join
([
str
(
i
)
for
i
in
self
.
stack
])
def
push
(
self
,
data
):
"""
pushes an item into the stack
returns -1 if the stack is empty
"""
if
len
(
self
.
stack
)
>=
self
.
limit
:
# indicates stack overflow
return
-
1
else
:
self
.
stack
.
append
(
data
)
def
pop
(
self
):
"""
pops the topmost item from the stack
returns -1 if the stack is empty
"""
if
len
(
self
.
stack
)
<=
0
:
# indicates stack underflow
return
-
1
else
:
return
self
.
stack
.
pop
()
def
peek
(
self
):
"""
returns the topmost element of the stack
returns -1 if the stack is empty
"""
if
len
(
self
.
stack
)
<=
0
:
# stack underflow
return
-
1
else
:
return
self
.
stack
[
len
(
self
.
stack
)
-
1
]
def
is_empty
(
self
):
"""
checks if the stack is empty
returns boolean value, True or False
"""
return
self
.
size
()
==
0
def
size
(
self
):
"""
returns the current size of the stack
"""
return
len
(
self
.
stack
)
@
staticmethod
def
get_code
():
"""
returns the code for current class
"""
return
inspect
.
getsource
(
Stack
)
class
InfixToPostfix
(
object
):
"""InfixToPostfix
get the postfix of the given infix expression
"""
def
__init__
(
self
,
expression
=
None
,
stack
=
None
):
"""
:param expression: the infix expression to be converted to postfix
:param stack: stack to perform infix to postfix operation
"""
self
.
expression
=
list
(
expression
)
self
.
my_stack
=
stack
@
staticmethod
def
_is_operand
(
char
):
"""
utility function to find whether the given character is an operator
"""
# OLD VERSION
# return ord(char) >= ord('a') and ord(char) <= ord('z') \
# or ord(char) >= ord('A') and ord(char) <= ord('Z')
return
True
if
ord
(
char
)
in
[
ord
(
c
)
for
c
in
ascii_letters
]
else
False
@
staticmethod
def
_precedence
(
char
):
"""
utility function to find precedence of the specified character
"""
if
char
==
'+'
or
char
==
'-'
:
return
1
elif
char
==
'*'
or
char
==
'/'
:
return
2
elif
char
==
'^'
:
return
3
else
:
return
-
1
def
infix_to_postfix
(
self
):
"""
function to generate postfix expression from infix expression
"""
postfix
=
[]
for
i
in
range
(
len
(
self
.
expression
)):
if
self
.
_is_operand
(
self
.
expression
[
i
]):
postfix
.
append
(
self
.
expression
[
i
])
elif
self
.
expression
[
i
]
==
'('
:
self
.
my_stack
.
push
(
self
.
expression
[
i
])
elif
self
.
expression
[
i
]
==
')'
:
top_operator
=
self
.
my_stack
.
pop
()
while
not
self
.
my_stack
.
is_empty
()
and
top_operator
!=
'('
:
postfix
.
append
(
top_operator
)
top_operator
=
self
.
my_stack
.
pop
()
else
:
while
not
self
.
my_stack
.
is_empty
()
and
self
.
_precedence
(
self
.
expression
[
i
])
<=
self
.
_precedence
(
self
.
my_stack
.
peek
()):
postfix
.
append
(
self
.
my_stack
.
pop
())
self
.
my_stack
.
push
(
self
.
expression
[
i
])
while
not
self
.
my_stack
.
is_empty
():
postfix
.
append
(
self
.
my_stack
.
pop
())
return
' '
.
join
(
postfix
)
@
staticmethod
def
get_code
():
"""
returns the code of the current class
"""
return
inspect
.
getsource
(
InfixToPostfix
)
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