string extension method - HasRepeatedCharacters

HasRepeatedCharacters.cs

namespace Extensions
{
    public static class StringExtensions
    {
        /// <summary>
        /// Check string for repeated characters
        /// </summary>
        /// <param name="str">string to check (the object being called on)</param>
        /// <returns>
        ///  <c>true</c> if the string has repeated characters otherwise, <c>false</c>.
        /// </returns>
        public static bool HasRepeatedCharacters(this string str)
        {
            var chars = str.ToCharArray();
            for (int i = 0; i < chars.Length; i++)
            {
                char c = chars[i];
                for (int j = 1; j < chars.Length; j++)
                {
                    if (j == i) { continue; }
                    if (c.Equals(chars[j])) { return true; }
                }
            }
            return false;
        }
    }
}