DAY 4 Q1 solved

Author: Aiyaan-Mahajan

Problems/Data-structures/Day-04/sol/Aiyaan_Mahajan/Q1sol.cpp

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+/*
+DAY 4
+Q1 Even Positions
+.*/
+
+#include <bits/stdc++.h>
+using namespace std;
+
+long long solve_case(string s) {
+    int n = s.size();
+
+    int fixedOpen = 0, fixedClose = 0;
+    for (char c : s) {
+        if (c == '(') fixedOpen++;
+        if (c == ')') fixedClose++;
+    }
+
+    int needOpen = n / 2 - fixedOpen;
+    int needClose = n / 2 - fixedClose;
+
+    int balance = 0;
+
+    // restore the string
+    for (int i = 0; i < n; ++i) {
+        if (s[i] == '(') balance++;
+        else if (s[i] == ')') balance--;
+        else {
+            // underscore -> choose bracket
+            if (needClose > 0 && balance > 0) {
+                s[i] = ')';
+                needClose--;
+                balance--;
+            } else {
+                s[i] = '(';
+                needOpen--;
+                balance++;
+            }
+        }
+    }
+
+    // compute cost
+    long long cost = 0;
+    stack<int> st;
+
+    for (int i = 0; i < n; ++i) {
+        if (s[i] == '(') st.push(i + 1);
+        else {
+            int openIdx = st.top(); st.pop();
+            cost += (i + 1) - openIdx;
+        }
+    }
+
+    return cost;
+}
+
+int main() {
+
+    int t; 
+    cin >> t;
+    while (t--) {
+        int n;
+        string s;
+        cin >> n >> s;
+        cout << solve_case(s) << "\n";
+    }
+    return 0;
+}
+
+//TC =O(n) and SC = O(n)
+/*
+My submission : https://codeforces.com/contest/1997/submission/355669016
+*/