From 88b6caa30aeb2d0e780039c13703af56c8ffdaa7 Mon Sep 17 00:00:00 2001 From: Ashwek Swamy <39827514+ashwek@users.noreply.github.com> Date: Fri, 1 Mar 2019 22:23:29 +0530 Subject: [PATCH] fixed balanced_parentheses, Added infix-prefix & postfix evaluation (#621) * Create infix_to_prefix_conversion.py * Create postfix_evaluation.py * Update balanced_parentheses.py --- .../stacks/infix_to_prefix_conversion.py | 61 +++++++++++++++++++ data_structures/stacks/postfix_evaluation.py | 50 +++++++++++++++ 2 files changed, 111 insertions(+) create mode 100644 data_structures/stacks/infix_to_prefix_conversion.py create mode 100644 data_structures/stacks/postfix_evaluation.py diff --git a/data_structures/stacks/infix_to_prefix_conversion.py b/data_structures/stacks/infix_to_prefix_conversion.py new file mode 100644 index 000000000..da5fc261f --- /dev/null +++ b/data_structures/stacks/infix_to_prefix_conversion.py @@ -0,0 +1,61 @@ +""" +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) +""" + +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 + + # Print table header for output + print('Symbol'.center(8), 'Stack'.center(print_width), 'Postfix'.center(print_width), sep = " | ") + print('-'*(print_width*3+7)) + + 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 + + print(x.center(8), (''.join(Stack)).ljust(print_width), (''.join(Postfix)).ljust(print_width), sep = " | ") # Output in tabular format + + 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 + + return "".join(Postfix) # return Postfix as str + +def infix_2_prefix(Infix): + Infix = list(Infix[::-1]) # reverse the infix equation + + for i in range(len(Infix)): + if(Infix[i] == '('): Infix[i] = ')' # change "(" to ")" + elif(Infix[i] == ')'): Infix[i] = '(' # change ")" to "(" + + return (infix_2_postfix("".join(Infix)))[::-1] # call infix_2_postfix on Infix, return reverse of Postfix + +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)") diff --git a/data_structures/stacks/postfix_evaluation.py b/data_structures/stacks/postfix_evaluation.py new file mode 100644 index 000000000..1786e71dd --- /dev/null +++ b/data_structures/stacks/postfix_evaluation.py @@ -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 +""" + +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))