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  1. #include <iostream>
  2. #include <stack>
  3. #include <string>
  4. #include <sstream>
  5. #include <vector>
  6. #include <cctype> // for isdigit
  7.  
  8. using namespace std;
  9.  
  10. bool isNumber(const string &s) {
  11.     if (s.empty()) return false;
  12.     size_t start = 0;
  13.     if (s[0] == '-') {
  14.         if (s.size() == 1) return false; // Only '-'
  15.         start = 1;
  16.     }
  17.     for (size_t i = start; i < s.size(); ++i) {
  18.         if (!isdigit(s[i])) {
  19.             return false;
  20.         }
  21.     }
  22.     return true;
  23. }
  24.  
  25. int main() {
  26.     int t;
  27.     cin >> t;
  28.     cin.ignore();
  29.  
  30.     while (t--) {
  31.         int n;
  32.         cin >> n;
  33.         cin.ignore();
  34.  
  35.         string line;
  36.         getline(cin, line);
  37.  
  38.         vector<string> tokens;
  39.         stringstream ss(line);
  40.         string token;
  41.         while (ss >> token) {
  42.             tokens.push_back(token);
  43.         }
  44.  
  45.         if (tokens.size() != n) {
  46.             cout << "Invalid Expression" << endl;
  47.             continue;
  48.         }
  49.  
  50.         stack<long long> st;
  51.         bool valid = true;
  52.  
  53.         for (int i = tokens.size() - 1; i >= 0; --i) {
  54.             string tok = tokens[i];
  55.  
  56.             if (isNumber(tok)) {
  57.                 st.push(stoll(tok));
  58.             } else if (tok == "+" || tok == "-" || tok == "*" || tok == "/") {
  59.                 if (st.size() < 2) {
  60.                     valid = false;
  61.                     break;
  62.                 }
  63.                 long long a = st.top(); st.pop();
  64.                 long long b = st.top(); st.pop();
  65.  
  66.                 if (tok == "+") st.push(a + b);
  67.                 else if (tok == "-") st.push(a - b);
  68.                 else if (tok == "*") st.push(a * b);
  69.                 else if (tok == "/") {
  70.                     if (b == 0) {
  71.                         valid = false;
  72.                         break;
  73.                     }
  74.                     st.push(a / b);
  75.                 }
  76.             } else {
  77.                 valid = false;
  78.                 break;
  79.             }
  80.         }
  81.  
  82.         if (valid && st.size() == 1) {
  83.             cout << st.top() << endl;
  84.         } else {
  85.             cout << "Invalid Expression" << endl;
  86.         }
  87.     }
  88.  
  89.     return 0;
  90. }
Success #stdin #stdout 0.01s 5288KB
comments (?)
stdin
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2
7
+ * - 5 4 100 20
3
- 4 7
stdout
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120
-3
https://ideone.com/S4lXk8
language:
C++ (gcc 8.3)
created:
3 days ago
visibility:
public

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