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fixed balanced_parentheses, Added infix-prefix & postfix evaluation #621

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Merged
poyea merged 3 commits into from
Mar 1, 2019
Merged

fixed balanced_parentheses, Added infix-prefix & postfix evaluation #621

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6d7e15b
Create infix_to_prefix_conversion.py
ashwek Nov 30, 2018
92f8271
Create postfix_evaluation.py
ashwek Nov 30, 2018
1b0fbe3
Update balanced_parentheses.py
ashwek Nov 30, 2018
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Create postfix_evaluation.py
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@ashwek
ashwek authored Nov 30, 2018
commit 92f8271e745e77abf52a564cb957ee94848c9e15
50 changes: 50 additions & 0 deletions data_structures/stacks/postfix_evaluation.py
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"""
Output:

Enter a Postfix Equation (space separated) = 5 6 9 * +
Symbol | Action | Stack
-----------------------------------
5 | push(5) | 5
6 | push(6) | 5,6
9 | push(9) | 5,6,9
| pop(9) | 5,6
| pop(6) | 5
* | push(6*9) | 5,54
| pop(54) | 5
| pop(5) |
+ | push(5+54) | 59

Result = 59
"""

import operator as op

def Solve(Postfix):
Stack = []
Div = lambda x, y: int(x/y) # integer division operation
Opr = {'^':op.pow, '*':op.mul, '/':Div, '+':op.add, '-':op.sub} # operators & their respective operation

# print table header
print('Symbol'.center(8), 'Action'.center(12), 'Stack', sep = " | ")
print('-'*(30+len(Postfix)))

for x in Postfix:
if( x.isdigit() ): # if x in digit
Stack.append(x) # append x to stack
print(x.rjust(8), ('push('+x+')').ljust(12), ','.join(Stack), sep = " | ") # output in tabular format
else:
B = Stack.pop() # pop stack
print("".rjust(8), ('pop('+B+')').ljust(12), ','.join(Stack), sep = " | ") # output in tabular format

A = Stack.pop() # pop stack
print("".rjust(8), ('pop('+A+')').ljust(12), ','.join(Stack), sep = " | ") # output in tabular format

Stack.append( str(Opr[x](int(A), int(B))) ) # evaluate the 2 values poped from stack & push result to stack
print(x.rjust(8), ('push('+A+x+B+')').ljust(12), ','.join(Stack), sep = " | ") # output in tabular format

return int(Stack[0])


if __name__ == "__main__":
Postfix = input("\n\nEnter a Postfix Equation (space separated) = ").split(' ')
print("\n\tResult = ", Solve(Postfix))