Python/data_structures/stacks/postfix_evaluation.py
Ashwek Swamy 88b6caa30a fixed balanced_parentheses, Added infix-prefix & postfix evaluation (#621)
* Create infix_to_prefix_conversion.py

* Create postfix_evaluation.py

* Update balanced_parentheses.py
2019-03-02 00:53:29 +08:00

51 lines
1.8 KiB
Python

"""
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))