feat: Added balanced parenthesis expression validation algorithm

strings/C++/Valid_parenthesis_expression.cpp

@@ -0,0 +1,46 @@
+#include <iostream>
+#include <string>
+#include <stack>
+using namespace std;
+
+class Solution {
+public:
+    bool checkValidString(string s) {
+        int n = s.length();
+        stack<int> open, star;
+        for (int i = 0; i < n; i++) {
+            if (s[i] == '(') open.push(i); // keeping track of where open brackets are.
+            else if (s[i] == '*') star.push(i); // and stars
+            else { // s[i]==')'
+                if (!open.empty()) open.pop(); // if open exists
+                else if (!star.empty()) star.pop(); // if star exists
+                else return false; // if none then invalid
+            }
+        }
+        // stack not empty meaning open parenthesis not closed
+        while (!open.empty()) {
+            if (star.empty()) return false; // no way to validate
+            else {
+                if (open.top() > star.top()) return false; // if star happened before open bracket
+                else {
+                    // star can be used as close
+                    star.pop();
+                    open.pop();
+                }
+            }
+        }
+        return true;
+    }
+};
+
+int main() {
+    Solution solution;
+    string input = "(*))";
+    bool isValid = solution.checkValidString(input);
+    if (isValid) {
+        cout << "The string is valid." << endl;
+    } else {
+        cout << "The string is not valid." << endl;
+    }
+    return 0;
+}