hactoberfest2022

Stacks & Queues/c++/postfix_expression.cpp

@@ -0,0 +1,45 @@
+#include <bits/stdc++.h>
+#include <stack>
+using namespace std;
+    int evalRPN(vector<string>& tokens) {
+        stack<int> st;
+
+        for(int i=0;i<tokens.size();i++){
+
+        if(tokens[i]=="+" || tokens[i]=="-" || tokens[i]=="*" || tokens[i]=="/"){
+              /// 2 elements
+             int v1 = st.top();
+            st.pop();
+            int v2 = st.top();
+            st.pop();
+
+            if(tokens[i]=="+"){
+                st.push(v2+v1);  /// push result inside stack
+            } 
+            else if(tokens[i]=="-"){
+                st.push(v2-v1);  /// push result inside stack
+            }
+             else if(tokens[i]=="*"){
+                st.push(v2*v1);  /// push result inside stack
+            }
+             else if(tokens[i]=="/"){
+                st.push(v2/v1);  /// push result inside stack
+            }
+        }
+
+        else {
+            /// operands
+            st.push(atoi(tokens[i].c_str()));
+        }
+    }
+
+    /// one element inside the stack
+
+        return st.top();
+    }       
+
+int main(){
+    vector<string>z={"2", "1", "+", "3", "*"};
+    cout<<"Answer is:"<<evalRPN(z)<<endl;
+    return 0;
+}