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Commit 62abce2

Browse files
program to convert infix to prefix made
1 parent 7e6e62e commit 62abce2

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1 file changed

+85
-53
lines changed

1 file changed

+85
-53
lines changed
Lines changed: 85 additions & 53 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,6 @@
11
#include<iostream>
22
#include<stack>
3+
#include<algorithm>
34
using namespace std;
45

56
/*Algorithm-
@@ -26,64 +27,95 @@ int getPriority(char c)
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return 0;
2728
}
2829

29-
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string InfixToPostfix(string infix)
30+
string infixToPostfix(string infix)
3131
{
32-
infix = '(' + infix + ')';
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string output="";
34-
int len = infix.size();
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stack<char>s;
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for(int i = 0 ; i < len; i++)
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{
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//if operand-add it to the postfix expression
40-
if(isalpha(infix[i]) || isdigit(infix[i]))
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output += infix[i];
42-
43-
//if opening brace then push it to stack
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else if(infix[i]=='(')
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s.push(infix[i]);
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else if(infix[i]==')')
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{
49-
while(s.top()!='(')
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{
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output += s.top();
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s.pop();
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}
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//remove ( from stack
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s.pop();
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}
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//if operator is found
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else
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{
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if(isOperator(s.top()))
64-
{
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while( getPriority(infix[i]) <= getPriority(s.top()))
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{
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output += s.top();
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s.pop();
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}
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//push current lower priority operator on stack
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s.push(infix[i]);
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}
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}
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}
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return output;
80-
32+
33+
int l = infix.size();
34+
stack<char> char_stack;
35+
string output;
36+
37+
for (int i = 0; i < l; i++) {
38+
39+
// If the scanned character is an
40+
// operand, add it to output.
41+
if (isalpha(infix[i]) || isdigit(infix[i]))
42+
output += infix[i];
43+
44+
// If the scanned character is an
45+
// ‘(‘, push it to the stack.
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else if (infix[i] == '(')
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char_stack.push('(');
48+
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// If the scanned character is an
50+
// ‘)’, pop and output from the stack
51+
// until an ‘(‘ is encountered.
52+
else if (infix[i] == ')') {
53+
54+
while (char_stack.top() != '(') {
55+
output += char_stack.top();
56+
char_stack.pop();
57+
}
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59+
// Remove '(' from the stack
60+
char_stack.pop();
61+
}
62+
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// Operator found
64+
else {
65+
66+
if (isOperator(char_stack.top())) {
67+
while (getPriority(infix[i])
68+
<= getPriority(char_stack.top())) {
69+
output += char_stack.top();
70+
char_stack.pop();
71+
}
72+
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// Push current Operator on stack
74+
char_stack.push(infix[i]);
75+
}
76+
}
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}
78+
return output;
8179
}
80+
81+
8282

83+
84+
string infixToPrefix(string infix)
85+
{
86+
/* Reverse String
87+
* Replace ( with ) and vice versa
88+
* Get Postfix
89+
* Reverse Postfix * */
90+
int l = infix.size();
91+
92+
// Reverse infix
93+
reverse(infix.begin(), infix.end());
94+
95+
// Replace ( with ) and vice versa
96+
for (int i = 0; i < l; i++) {
97+
98+
if (infix[i] == '(') {
99+
infix[i] = ')';
100+
i++;
101+
}
102+
else if (infix[i] == ')') {
103+
infix[i] = '(';
104+
i++;
105+
}
106+
}
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108+
string prefix = infixToPostfix(infix);
109+
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// Reverse postfix
111+
reverse(prefix.begin(), prefix.end());
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113+
return prefix;
114+
}
83115

84116
int main()
85117
{
86-
string s= InfixToPostfix("A*B+C/D");
87-
cout<<s;
118+
string s = "(A*B+C/D)";
119+
cout<<infixToPostfix(s);
88120
return 0;
89121
}

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