1.1 Is Unique

[rmorabia]

Implement an algorithm to determine if a string has all unique characters. What if you cannot use additional data structures?

[megantaylor]

https://repl.it/@megantaylor/IsUnique

//with data structure
function uniqueChars(str) {
  let charObj = {};
  for(let i = 0; i < str.length; i++) {
    let char = str[i];
    if(charObj[char]) return false; else charObj[char] = true;
  }
  return true;
}

// no data structures 
function uniqueCharsNoDataStructure(string) {
  for (let i = 0; i < string.length; i++) {
    for (let j = i + 1; j < string.length; j++) {
      if (string[i] === string[j]) {
        return false;
      }
    }
  }
  return true;
};

[rmorabia]

https://repl.it/@rmorabia/CalmInsidiousAddons

function cool(string) {
  for (let i = 0; i < string.length; i++) { 
    let count = 0
    for (let z = 0; z < string.length; z++) {
      if (string[z] === string[i]) { 
        count++
        if (count >= 2) {
          return false
        }
      }
    }
  }
  return true
}

cool('straddle')
cool('stradle')

[lpatmo]

https://repl.it/@lpatmo/FussyMiserlyMedia

// Implement an algorithm to determine if a string has all unique characters. What if you
// cannot use additional data structures? 

/****** SOLUTION 1 *******/
function isUnique1(str) {
  //loop through string
  //check if each letter is unique
  console.log(str)
  let holder = {};
  for (var i = 0; i < str.length; i++) {
    if (holder[str[i]]) {
      console.log('false')
      return false;
    } else {
      holder[str[i]] = 1;
    }
  }
  console.log(holder);
  return true;
  
}
//console.log(isUnique2('helo'));

/****** SOLUTION 2 *******/

function isUnique2(str) {
  //loop through string
  //check if each letter is unique
  if (str.length < 2) {
    return true;
  }
  for (var left=0; left< str.length; left++) {
    console.log(left)
    for (var right = left+1; right < str.length; right++) {
       if (str[left] === str[right]) {
         return false;
       } 
    }
  }
  return true;
  
}
//console.log(isUnique2('helo'));

Time complexity:  nlogn?

/****** SOLUTION 3 *******/

function isUnique3(str) {
  //use Sets
  //check if each letter is unique
  return new Set(str).length !== str.length;
}
console.log(isUnique3('helo'));