Performance tips for O(n²) on JavaScript iterations.

iteration_of_collections.js

function charUnique(s) {
  var r = {},
    i, x;
  for (i = s.length - 1; i > -1; i--) {
    x = s[i];
    if (r[x])
      return false;
    r[x] = true;
  }
  return true;
}

function charIndexOfUnique(s) {
  var r = [],
    i, x;
  for (i = s.length - 1; i > -1; i--) {
    x = s[i];
    if (r.indexOf(x)>0)
      return false;
    r.push[x];
  }
  
  return true;
}

function charCodeUnique(s) {
  var r = [],
    i, x;
  for (i = s.length - 1; i > -1; i--) {
    x = s.charCodeAt(i);
    if (r[x])
      return false;
    r[x] = true;
  }
  
  return true;
}

function timer(f) {
  var i;
  var t0;

  var string = [];
  for (i = 32; i < 127; i++)
    string[string.length] = String.fromCharCode(i);
  string = string.join('');
  console.time("start")
  for (i = 0; i < 10000; i++)
    f(string);
  console.timeEnd("start")
}

timer(charUnique);
// 86 ms
timer(charIndexOfUnique);
// 24 ms
timer(charCodeUnique)
// 12 ms