Reverse Array in Place

Reverse Array in Place

Reverse an array in place.

• do not push elements into new array
• do not use array.reverse() method

Javascript Reverse Array in Place

function reverseArrayInPlace(arr) {
  // loop over half items in array and switch out opposite counterpart
  // input: [ 1, 2, 3, 4 ] <--- 4 items -> cut in half -> 2 loops
  // loop 1: switch [ *1*, 2, 3, *4* ] // [ 4, 2, 3, 1 ]
  // loop 2: switch [ 4, *2*, *3*, 1 ] // [ 4, 3, 2, 1 ]

  for (let i = 0; i < arr.length / 2; i++) {
    let tempVar = arr[i];
    arr[i] = arr[arr.length - 1 - i];
    arr[arr.length - 1 - i] = tempVar;
  }

  return arr;
}

// length is odd number
reverseArrayInPlace([1, 2, 3, 4, 5]); // $: [ 5, 4, 3, 2, 1 ]

// length is even number
reverseArrayInPlace([1, 2, 3, 4]); // $: [ 4, 3, 2, 1 ]