Flipping bits - RunTime: o(n), Space: o(n)

compare-swap.js

// Start with: ['a', 'b', 'c', 'd', 'e']
// End with: ['a', 'b', 'c', 'd', 'e']
// without using any additional variables, and within o(n) runtime.

// swapArr (reference Array, pointer 1, pointer 2)
// will take the reference to the position within the array
// and swap them without using a third variable
const swapArr = (arr, x,y) => {
  // replace ASCII values with the character decimals
  arr[x] = arr[x].charCodeAt(0);
  arr[y] = arr[y].charCodeAt(0);

  // do a XOR bitwise comparison & swap
  arr[x] = arr[x]^arr[y];
  arr[y] = arr[x]^arr[y];
  arr[x] = arr[x]^arr[y];

  // switch the characters back to the ASCII values
  arr[x] = String.fromCharCode(arr[x]);
  arr[y] = String.fromCharCode(arr[y]);
  return arr;
}

const main = () => {
  let _arr = ['a','b','c','d','e'];
  console.log(`Before: ${_arr}`);

  // start pointers at beginning and end of array
  // then loop until we meet in the middle
  let n = _arr.length;
  let s = 0;
  let e = n - 1;
  while (s < e) {
    // swap the letters
    _arr = swapArr(_arr, s, e);
    s++;
    e--;
  }
  console.log(`After: ${_arr}`);
}

// runner function
main();