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infix2Prefix.cpp
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infix2Prefix.cpp
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#include<bits/stdc++.h>
using namespace std;
int prec( char c){
if(c=='^'){
return 3;
}
else if(c=='*'|| c=='/'){
return 2;
}
else if(c=='+'|| c=='-'){
return 1;
}
else{
return -1;
}
}
string infix2Prefix( string s){
//reverse(s.begin(),s.end());
stack<char> st;
string res;
for(int i=s.length()-1;i>=0;i--){
if(s[i]>='a' && s[i]<='z' || s[i]>='A' && s[i]<='z'){
res+=s[i];
}
else if(s[i]==')'){
st.push(s[i]);
}
else if(s[i]=='('){
while(!st.empty() && st.top()!=')'){
res+=st.top();
st.pop();
}
if(!st.empty()){
st.pop();
}
}
else{
while (!st.empty() && prec(st.top())>=prec(s[i]))
{
res+=st.top();
st.pop();
}
st.push(s[i]);
}
}
while(!st.empty()){
res+=st.top();
st.pop();
}
// reverse(s.begin(),s.end());
return res;
}
int main(){
string s="(a-b/c)*(a/k-l)";
cout<<infix2Prefix(s)<<endl;
return 0;
}