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prefix_postfix_infix.cpp
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prefix_postfix_infix.cpp
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#include<iostream>
#include<stack>
using namespace std;
int postfix_evalution(string s){
stack<int> st;
int i=0;
while(i<s.length()){
if(s[i]>='0' && s[i]<='9'){
st.push(s[i]-'0');
}
else{
int b=st.top();
st.pop();
int a=st.top();
st.pop();
if(s[i]=='+')st.push(a+b);
else if(s[i]=='-')st.push(a-b);
else if(s[i]=='*')st.push(a*b);
else if(s[i]=='/')st.push(a/b);
}
i++;
}
return st.top();
}
int prefix_evalution(string s){
stack<int> st;
for(int i=s.length()-1;i>=0;i--){
if(s[i]>='0' && s[i]<='9'){
st.push(s[i]-'0');
}
else{
int a=st.top();
st.pop();
int b=st.top();
st.pop();
if(s[i]=='+')st.push(a+b);
else if(s[i]=='-')st.push(a-b);
else if(s[i]=='*')st.push(a*b);
else if(s[i]=='/')st.push(a/b);
}
}
return st.top();
}
int prec(char c){
if(c=='+' || c=='-')return 1;
else if(c=='*' || c=='/')return 2;
else if(c=='^') return 3;
return -1;
}
string infix_to_postfix(string s){
stack<char> st;
string ans="";
for(int i=0;i<s.length();i++){
if(s[i]=='(')st.push(s[i]);
else if(s[i]==')'){
while(st.top()!='('){
ans+=st.top();
st.pop();
}
st.pop();
}
else if(s[i]-'a'>=0 && s[i]-'a'<26)ans+=s[i];
else{
if(st.empty() || st.top()=='(' || prec(s[i])> prec(st.top())){
st.push(s[i]);
}
else{
ans+=st.top();
st.pop();
st.push(s[i]);
}
}
}
while(!st.empty()){
ans+=st.top();
st.pop();
}
return ans;
}
string infix_to_prefix(string s){
string ans="";
stack<char> st;
for(int i=s.length()-1;i>=0;i--){
if(s[i]==')'){
st.push(s[i]);
}
else if(s[i]-'a'>=0 && s[i]-'a'<26)ans=s[i]+ans;
else if(s[i]=='('){
while(st.top()!=')'){
ans=st.top()+ans;
st.pop();
}
st.pop();
}
else{
if(st.empty()||st.top()==')'||prec(st.top())<=prec(s[i])){
st.push(s[i]);
}
else{
ans=st.top()+ans;
st.pop();
st.push(s[i]);
}
}
}
while(!st.empty()){
ans=st.top()+ans;
st.pop();
}
return ans;
}
int main(){
cout<<postfix_evalution("46+2/5*7+")<<endl;
cout<<prefix_evalution("-+7*45+20")<<endl;
cout<<infix_to_postfix("(a-b/c)*(a/k-l)")<<endl;
cout<<infix_to_prefix("(a-b/c)*(a/k-l)")<<endl;
return 0;
}