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Fix bug and edit doctests for infix_to_prefix_conversion (TheAlgorithms#10259)
* Fix bug and edit doctests * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * Add type hints, raiseError and other minor adjustments * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * Cleaning code * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci --------- Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
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‎data_structures/stacks/infix_to_prefix_conversion.py

+64-37
Original file line numberDiff line numberDiff line change
@@ -15,7 +15,7 @@
1515
"""
1616

1717

18-
def infix_2_postfix(infix):
18+
def infix_2_postfix(infix: str) -> str:
1919
"""
2020
>>> infix_2_postfix("a+b^c") # doctest: +NORMALIZE_WHITESPACE
2121
Symbol | Stack | Postfix
@@ -28,22 +28,35 @@ def infix_2_postfix(infix):
2828
| + | abc^
2929
| | abc^+
3030
'abc^+'
31-
>>> infix_2_postfix("1*((-a)*2+b)")
32-
Traceback (most recent call last):
33-
...
34-
KeyError: '('
31+
32+
>>> infix_2_postfix("1*((-a)*2+b)") # doctest: +NORMALIZE_WHITESPACE
33+
Symbol | Stack | Postfix
34+
-------------------------------------------
35+
1 | | 1
36+
* | * | 1
37+
( | *( | 1
38+
( | *(( | 1
39+
- | *((- | 1
40+
a | *((- | 1a
41+
) | *( | 1a-
42+
* | *(* | 1a-
43+
2 | *(* | 1a-2
44+
+ | *(+ | 1a-2*
45+
b | *(+ | 1a-2*b
46+
) | * | 1a-2*b+
47+
| | 1a-2*b+*
48+
'1a-2*b+*'
49+
3550
>>> infix_2_postfix("")
3651
Symbol | Stack | Postfix
3752
----------------------------
3853
''
39-
>>> infix_2_postfix("(()") # doctest: +NORMALIZE_WHITESPACE
40-
Symbol | Stack | Postfix
41-
----------------------------
42-
( | ( |
43-
( | (( |
44-
) | ( |
45-
| | (
46-
'('
54+
55+
>>> infix_2_postfix("(()")
56+
Traceback (most recent call last):
57+
...
58+
ValueError: invalid expression
59+
4760
>>> infix_2_postfix("())")
4861
Traceback (most recent call last):
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...
@@ -59,7 +72,7 @@ def infix_2_postfix(infix):
5972
"+": 1,
6073
"-": 1,
6174
} # Priority of each operator
62-
print_width = len(infix) if (len(infix) > 7) else 7
75+
print_width = max(len(infix), 7)
6376

6477
# Print table header for output
6578
print(
@@ -76,14 +89,17 @@ def infix_2_postfix(infix):
7689
elif x == "(":
7790
stack.append(x) # if x is "(" push to Stack
7891
elif x == ")": # if x is ")" pop stack until "(" is encountered
92+
if len(stack) == 0: # close bracket without open bracket
93+
raise IndexError("list index out of range")
94+
7995
while stack[-1] != "(":
8096
post_fix.append(stack.pop()) # Pop stack & add the content to Postfix
8197
stack.pop()
8298
else:
8399
if len(stack) == 0:
84100
stack.append(x) # If stack is empty, push x to stack
85101
else: # while priority of x is not > priority of element in the stack
86-
while len(stack) > 0 and priority[x] <= priority[stack[-1]]:
102+
while stack and stack[-1] != "(" and priority[x] <= priority[stack[-1]]:
87103
post_fix.append(stack.pop()) # pop stack & add to Postfix
88104
stack.append(x) # push x to stack
89105

@@ -95,6 +111,9 @@ def infix_2_postfix(infix):
95111
) # Output in tabular format
96112

97113
while len(stack) > 0: # while stack is not empty
114+
if stack[-1] == "(": # open bracket with no close bracket
115+
raise ValueError("invalid expression")
116+
98117
post_fix.append(stack.pop()) # pop stack & add to Postfix
99118
print(
100119
" ".center(8),
@@ -106,7 +125,7 @@ def infix_2_postfix(infix):
106125
return "".join(post_fix) # return Postfix as str
107126

108127

109-
def infix_2_prefix(infix):
128+
def infix_2_prefix(infix: str) -> str:
110129
"""
111130
>>> infix_2_prefix("a+b^c") # doctest: +NORMALIZE_WHITESPACE
112131
Symbol | Stack | Postfix
@@ -119,10 +138,23 @@ def infix_2_prefix(infix):
119138
| | cb^a+
120139
'+a^bc'
121140
122-
>>> infix_2_prefix("1*((-a)*2+b)")
123-
Traceback (most recent call last):
124-
...
125-
KeyError: '('
141+
>>> infix_2_prefix("1*((-a)*2+b)") # doctest: +NORMALIZE_WHITESPACE
142+
Symbol | Stack | Postfix
143+
-------------------------------------------
144+
( | ( |
145+
b | ( | b
146+
+ | (+ | b
147+
2 | (+ | b2
148+
* | (+* | b2
149+
( | (+*( | b2
150+
a | (+*( | b2a
151+
- | (+*(- | b2a
152+
) | (+* | b2a-
153+
) | | b2a-*+
154+
* | * | b2a-*+
155+
1 | * | b2a-*+1
156+
| | b2a-*+1*
157+
'*1+*-a2b'
126158
127159
>>> infix_2_prefix('')
128160
Symbol | Stack | Postfix
@@ -134,26 +166,21 @@ def infix_2_prefix(infix):
134166
...
135167
IndexError: list index out of range
136168
137-
>>> infix_2_prefix('())') # doctest: +NORMALIZE_WHITESPACE
138-
Symbol | Stack | Postfix
139-
----------------------------
140-
( | ( |
141-
( | (( |
142-
) | ( |
143-
| | (
144-
'('
169+
>>> infix_2_prefix('())')
170+
Traceback (most recent call last):
171+
...
172+
ValueError: invalid expression
145173
"""
146-
infix = list(infix[::-1]) # reverse the infix equation
174+
reversed_infix = list(infix[::-1]) # reverse the infix equation
147175

148-
for i in range(len(infix)):
149-
if infix[i] == "(":
150-
infix[i] = ")" # change "(" to ")"
151-
elif infix[i] == ")":
152-
infix[i] = "(" # change ")" to "("
176+
for i in range(len(reversed_infix)):
177+
if reversed_infix[i] == "(":
178+
reversed_infix[i] = ")" # change "(" to ")"
179+
elif reversed_infix[i] == ")":
180+
reversed_infix[i] = "(" # change ")" to "("
153181

154-
return (infix_2_postfix("".join(infix)))[
155-
::-1
156-
] # call infix_2_postfix on Infix, return reverse of Postfix
182+
# call infix_2_postfix on Infix, return reverse of Postfix
183+
return (infix_2_postfix("".join(reversed_infix)))[::-1]
157184

158185

159186
if __name__ == "__main__":

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