['a', 'b', 'c', 'd', 'e']

['a', 'e', 'd', 'c']

['c', 'c', 'c', 'c']

['a', 'b', 'e', 'd']

all combinations =   [`aaa`, `aab`, `aac`
                      `aba`, `abb`, `abc`
                      `aca`, `acb`, `acc`
                      `baa`, `bab`, `bac`
                      `bba`, `bbb`, `bbc`
                      `bca`, `bcb`, `bcc`
                      `caa`, `cab`, `cac`
                      `cba`, `cbb`, `cbc`
                      `cca`, `ccb`, `ccc`]

sorted combinations = [`aaa`, `aab`, `aac`
                       `aab`, `abb`, `abc`
                       `aac`, `abc`, `acc`
                       `aab`, `abb`, `abc`
                       `abb`, `bbb`, `bbc`
                       `abc`, `bbc`, `bcc`
                       `aac`, `abc`, `acc`
                       `abc`, `bbc`, `bcc`
                       `acc`, `bcc`, `ccc`]

remove duplicates  = [`aaa`, `aab`, `aac`,
                      `abb`, `abc`, `acc`,
                      `bbb`, `bbc`, `bcc`,
                      `ccc`]

then choose from these with equal probability of 1/10

function generateRandomOrExtremeSet(a) {
   var n = Math.random();
   var set = [];
   if (n > 0.5)
      for (var i = 0; i < a.length; ++i)
         set[i] = a[Math.round(Math.random()*(a.length-1))];
   else {
      var index  = Math.round(Math.random() * (a.length-1));
      for (var i = 0; i < a.length; ++i) {
         if (Math.random() > 0.8) // change to adjust extremeness
            set[i] = a[Math.round(Math.random()*(a.length-1))];
         else
            set[i] = a[index];
      }
   }
   return set;
}