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fixed balanced_parentheses, Added infix-prefix & postfix evaluation (T…
…heAlgorithms#621) * Create infix_to_prefix_conversion.py * Create postfix_evaluation.py * Update balanced_parentheses.py
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Original file line number | Diff line number | Diff line change |
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""" | ||
Output: | ||
Enter an Infix Equation = a + b ^c | ||
Symbol | Stack | Postfix | ||
---------------------------- | ||
c | | c | ||
^ | ^ | c | ||
b | ^ | cb | ||
+ | + | cb^ | ||
a | + | cb^a | ||
| | cb^a+ | ||
a+b^c (Infix) -> +a^bc (Prefix) | ||
""" | ||
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def infix_2_postfix(Infix): | ||
Stack = [] | ||
Postfix = [] | ||
priority = {'^':3, '*':2, '/':2, '%':2, '+':1, '-':1} # Priority of each operator | ||
print_width = len(Infix) if(len(Infix)>7) else 7 | ||
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# Print table header for output | ||
print('Symbol'.center(8), 'Stack'.center(print_width), 'Postfix'.center(print_width), sep = " | ") | ||
print('-'*(print_width*3+7)) | ||
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for x in Infix: | ||
if(x.isalpha() or x.isdigit()): Postfix.append(x) # if x is Alphabet / Digit, add it to Postfix | ||
elif(x == '('): Stack.append(x) # if x is "(" push to Stack | ||
elif(x == ')'): # if x is ")" pop stack until "(" is encountered | ||
while(Stack[-1] != '('): | ||
Postfix.append( Stack.pop() ) #Pop stack & add the content to Postfix | ||
Stack.pop() | ||
else: | ||
if(len(Stack)==0): Stack.append(x) #If stack is empty, push x to stack | ||
else: | ||
while( len(Stack) > 0 and priority[x] <= priority[Stack[-1]]): # while priority of x is not greater than priority of element in the stack | ||
Postfix.append( Stack.pop() ) # pop stack & add to Postfix | ||
Stack.append(x) # push x to stack | ||
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print(x.center(8), (''.join(Stack)).ljust(print_width), (''.join(Postfix)).ljust(print_width), sep = " | ") # Output in tabular format | ||
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while(len(Stack) > 0): # while stack is not empty | ||
Postfix.append( Stack.pop() ) # pop stack & add to Postfix | ||
print(' '.center(8), (''.join(Stack)).ljust(print_width), (''.join(Postfix)).ljust(print_width), sep = " | ") # Output in tabular format | ||
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return "".join(Postfix) # return Postfix as str | ||
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def infix_2_prefix(Infix): | ||
Infix = list(Infix[::-1]) # reverse the infix equation | ||
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for i in range(len(Infix)): | ||
if(Infix[i] == '('): Infix[i] = ')' # change "(" to ")" | ||
elif(Infix[i] == ')'): Infix[i] = '(' # change ")" to "(" | ||
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return (infix_2_postfix("".join(Infix)))[::-1] # call infix_2_postfix on Infix, return reverse of Postfix | ||
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if __name__ == "__main__": | ||
Infix = input("\nEnter an Infix Equation = ") #Input an Infix equation | ||
Infix = "".join(Infix.split()) #Remove spaces from the input | ||
print("\n\t", Infix, "(Infix) -> ", infix_2_prefix(Infix), "(Prefix)") |
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,50 @@ | ||
""" | ||
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 | ||
""" | ||
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import operator as op | ||
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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 | ||
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# print table header | ||
print('Symbol'.center(8), 'Action'.center(12), 'Stack', sep = " | ") | ||
print('-'*(30+len(Postfix))) | ||
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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 | ||
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A = Stack.pop() # pop stack | ||
print("".rjust(8), ('pop('+A+')').ljust(12), ','.join(Stack), sep = " | ") # output in tabular format | ||
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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 | ||
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return int(Stack[0]) | ||
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if __name__ == "__main__": | ||
Postfix = input("\n\nEnter a Postfix Equation (space separated) = ").split(' ') | ||
print("\n\tResult = ", Solve(Postfix)) |