isBothPrefixAndSuffix

main.cpp

// checks if target string has key string as both prefix and suffix
bool isBothPrefixAndSuffix(string &target, string &key) {
  int n = target.length(), m = key.length();
  // target must be at least twice as long as key
  if (n < m * 2) {
    return false;
  }
  int lt = 0, rt = target.length() - 1, lk = 0, rk = key.length() - 1;
  while (lk < m) {
    if (key[lk] != target[lt] || key[rk] != target[rt]) {
      return false;
    }
    ++lt; ++lk; --rt; --rk;
  }
  return true;
}