Infix-to-Prefix-Convertion-by-Python
def isOperator(c): return (not (c >= 'a' and c <= 'z') and not(c >= '0' and c <= '9') and not(c >= 'A' and c <= 'Z'))
def getPriority(C): if (C == '-' or C == '+'): return 1 elif (C == '*' or C == '/'): return 2 elif (C == '^'): return 3 return 0
def infixToPrefix(infix): operators = [] operands = []
for i in range(len(infix)):
if (infix[i] == '(' ):
operators.append(infix[i])
elif (infix[i] == ')'):
while (len(operators)!=0 and (operators[-1] != '(' )):
op1 = operands[-1]
operands.pop()
op2 = operands[-1]
operands.pop()
op = operators[-1]
operators.pop()
tmp = op + op2 + op1
operands.append(tmp)
operators.pop()
elif (not isOperator(infix[i])):
operands.append(infix[i] + "")
else:
while (len(operators)!=0 and getPriority(infix[i]) <= getPriority(operators[-1])):
op1 = operands[-1]
operands.pop()
op2 = operands[-1]
operands.pop()
op = operators[-1]
operators.pop()
tmp = op + op2 + op1
operands.append(tmp)
operators.append(infix[i])
while (len(operators)!=0):
op1 = operands[-1]
operands.pop()
op2 = operands[-1]
operands.pop()
op = operators[-1]
operators.pop()
tmp = op + op2 + op1
operands.append(tmp)
return operands[-1]
while(1): s = input("Infix Expression : ") print("Prefix Expression : ", infixToPrefix(s))
Step 1: Reverse the infix string. Note that while reversing the string you must interchange left and right parentheses. Step 2: Obtain the postfix expression of the infix expression Step 1. Step 3: Reverse the postfix expression to get the prefix expression
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