cxx17/cc14.cc

// Determine if a string has all-unique characters.

#define CATCH_CONFIG_MAIN
#include <catch.hpp>

#include <experimental/string_view>
#include <range/v3/all.hpp>
#include <string>
#include <unordered_map>

using namespace ranges;

bool is_odd(int v) { return (v % 2) == 1; }

bool palindrome(std::experimental::string_view src) {
  std::unordered_map<char, int> count;

  int nchars = 0;

  // Done to test range comprehensions.  Not really any better than
  // the procedural version.
  for (auto ch :
       src | view::filter([](char ch) { return std::isalpha(ch); }) |
           view::transform([](char ch) { return std::tolower(ch); })) {
    count[ch]++;
    nchars++;
  }

  int singles = 0;
  int odds = 0;

  // TODO(michaelh): try as a filter.
  for (auto c : count | view::values) {
    if (c == 1) {
      singles++;
    }
    if (is_odd(c)) {
      odds++;
    }
  }

  if (is_odd(nchars)) {
    return singles == 1 && odds == 1;
  } else {
    return singles == 0 && odds == 0;
  }
}

TEST_CASE("cc14", "palindrome") {
  REQUIRE(palindrome("Taco Cat") == true);
  REQUIRE(palindrome("Tact Coa") == true);
  REQUIRE(palindrome("Happy") == false);
  REQUIRE(palindrome("Pant") == false);
}