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  1. #include <vector>
  2. #include <string>
  3. #include <iostream>
  4.  
  5. static const std::vector<std::string> EXAMPLES = {
  6.     	"({[{}]{}[]})",
  7.         "({}}{[{}]{}[]})",
  8.         "({[{}]{}[]}",
  9.         "({[{}]{}]})",
  10.         "({[{}{}[]})",
  11.         "",
  12.         "{}",
  13.         "(i (am so [lispish]))",
  14. };
  15.  
  16. static const char eof = char(-1);
  17. static const std::string open_braces  = "({[";
  18. static const std::string close_braces = ")}]";
  19.  
  20. inline char matching_brace(char c)
  21. {
  22.     const std::size_t i = close_braces.find(c);
  23.     return i != std::string::npos ? open_braces[i] : eof;
  24. }
  25.  
  26. static bool is_balanced(const std::string &s)
  27. {
  28.     std::string brace_stack;
  29.  
  30.     for (auto c : s) {
  31.         if (open_braces.find(c) != std::string::npos) {
  32.             brace_stack.push_back(c);
  33.             continue;
  34.         }
  35.  
  36.         const char pair = matching_brace(c);
  37.         if (pair != eof) {
  38.             if (!brace_stack.empty() && brace_stack.back() == pair) {
  39.                 brace_stack.pop_back();
  40.             } else {
  41.                 return false;
  42.             }
  43.         }
  44.     }
  45.  
  46.     return brace_stack.empty();
  47. }
  48.  
  49. int main()
  50. {
  51.     std::cout << std::boolalpha;
  52.     for (const auto & e : EXAMPLES) {
  53.         std::cout << is_balanced(e) << "\n";
  54.     }
  55.     return 0;
  56. }
Success #stdin #stdout 0s 3432KB
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stdin
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Standard input is empty
stdout
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true
false
false
false
false
true
true
true
https://ideone.com/wZv8AD
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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