How to determine if a string contains only unique characters in JavaScript

Here are two ways to determine whether a string contains unique characters in JavaScript.

• Hashmap solution:

  • Space complexity: O(n)
  • Time complexity: O(n)

• Bit solution:

  • Space complexity: O(1)
  • Time complexity: O(n)

The bit solution can be likened to a mold of amber. Each letter carries a different bit signature. If we hold onto a variable that retains a 1 for each different character. If there ever is a case where that variable and the current character we are on overlap, that means we do not have a unique character and can return false.

Another approach could involve 2 for loops or sorting the string and checking it’s neighbor.
or another space efficient approach (at the expense of time) could involve using indexOf.

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function isUniqueMapWise(string) {
  let isUnique = true;
  const chars = string
                .split('')
                .reduce((map, char) => {
                  if (map[char]) {
                    map[char]++;
                    isUnique = false;
                  } else {
                    map[char] = 1;
                  }
                  return map;
                }, {});
  
  return isUnique;
}
function isUniqueBitwise(string) {
    let checker = 0;
    for (let i = 0; i < string.length; i++) {
        const value = string.charCodeAt(i) - 'a'.charCodeAt(0);
        if ((checker & (1 << value)) > 0) return false;
        checker |= (1 << value);
    }
    return true;
}

Tests can be found at REPL.it