forked from Sangwan5688/Hacktoberfest2021
-
Notifications
You must be signed in to change notification settings - Fork 0
/
infix_to_prefix.cpp
112 lines (101 loc) · 2.72 KB
/
infix_to_prefix.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
#include <iostream>
#include <stack>
#include <algorithm>
using namespace std;
bool isOperator(char c)
{
if (c == '+' || c == '-' || c == '*' || c == '/' || c == '^') {
return true;
}
else {
return false;
}
}
int precedence(char c)
{
if (c == '^')
return 3;
else if (c == '*' || c == '/')
return 2;
else if (c == '+' || c == '-')
return 1;
else
return -1;
}
string InfixToPrefix(stack<char> s, string infix)
{
string prefix;
reverse(infix.begin(), infix.end());
for (int i = 0; i < infix.length(); i++) {
if (infix[i] == '(') {
infix[i] = ')';
}
else if (infix[i] == ')') {
infix[i] = '(';
}
}
for (int i = 0; i < infix.length(); i++) {
if ((infix[i] >= 'a' && infix[i] <= 'z') || (infix[i] >= 'A' && infix[i] <= 'Z')) {
prefix += infix[i];
}
else if (infix[i] == '(') {
s.push(infix[i]);
}
else if (infix[i] == ')') {
while ((s.top() != '(') && (!s.empty())) {
prefix += s.top();
s.pop();
}
if (s.top() == '(') {
s.pop();
}
}
else if (isOperator(infix[i])) {
if (s.empty()) {
s.push(infix[i]);
}
else {
if (precedence(infix[i]) > precedence(s.top())) {
s.push(infix[i]);
}
else if ((precedence(infix[i]) == precedence(s.top()))
&& (infix[i] == '^')) {
while ((precedence(infix[i]) == precedence(s.top()))
&& (infix[i] == '^')) {
prefix += s.top();
s.pop();
}
s.push(infix[i]);
}
else if (precedence(infix[i]) == precedence(s.top())) {
s.push(infix[i]);
}
else {
while ((!s.empty()) && (precedence(infix[i]) < precedence(s.top()))) {
prefix += s.top();
s.pop();
}
s.push(infix[i]);
}
}
}
}
while (!s.empty()) {
prefix += s.top();
s.pop();
}
reverse(prefix.begin(), prefix.end());
return prefix;
}
int main()
{
string infix, prefix;
cout << "Enter a Infix Expression :" << endl;
cin >> infix;
stack<char> stack;
cout << "INFIX EXPRESSION: " << infix << endl;
prefix = InfixToPrefix(stack, infix);
cout << endl
<< "PREFIX EXPRESSION: " << prefix<<"\n";
return 0;
}