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Javascript – Reverse the second half of array elements in js

Here, I have written a program that traverses and reverses the last part of the array elements, like if the array is [5, 17, 11, 10, 12, 6], and I want output like [5, 17, 11, 6, 12, 10], so I have written a program, but the output is not coming out as expected. Can you please check and modify that so that I will get the desired result?

let a = [5, 17, 11, 10, 12, 6];
let n = a.length;
for (let i = 0, j = (n / 2) - 1; i < n / 4; i++, j--) {
  let temp = a[n / 2 + i];
  a[n / 2 + i] = a[j];
  a[j] = temp;

}

for (i = 0; i < n; i++) {
  console.log(a[i])
}
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3

Answers


  1. 0

    No need for all the extra rigmarole you’ve got to loop over Array elements – instead, splice() the original array halfway, reverse() the spliced values, then push() them all back into a.

    let a = [5, 17, 11, 10, 12, 6];
let b = a.splice(a.length / 2).reverse();
a.push(...b);
console.log(a); // [5, 17, 11, 6, 12, 10]

    As I mentioned in my comment – be forewarned that this will not function the way you seemingly want it to if a.length % 2 != 0, so you may consider using Math.floor() on the calculation of a.length / 2 – the acceptability of this will depend on your requirements and constraints.`

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  2. 0

    You can divide the array in two parts and reverse the secondHalf using the reverse js method.

    If you don’t want to use the reverse you can follow this approach:

    const array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const half = Math.ceil(array.length / 2);

let firstHalf = array.splice(0, half);
let secondHalf = array.splice(-half);
let secondHalfReversed = [];

for (let i = secondHalf.length - 1; i >= 0; i--) {
  secondHalfReversed.push(secondHalf[i]);
}

const finalArray = [...firstHalf, ...secondHalfReversed];

console.log(finalArray);
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  3. 0

    This is similar to @esqew but a version that doesn’t mutate the original array..

    And his comments on none even array lengths still applies here.

    let a = [5, 17, 11, 10, 12, 6];
let h = a.length / 2;
let r = [
  ...a.slice(0, h),
  ...a.slice(h).reverse()
];

console.log(r); // [5, 17, 11, 6, 12, 10]
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