akbhairwal

Posted on Sep 24, 2019

6-10PM challenge problem #001

#challenge #programming #problem #interview

Move Zeros To End

An array 'arr' which have integers. You need to move all the zeros in the end of the array. You should preserve the relative order of other numbers in the array.

We should implement a solution that is more efficient than a naive brute force.

Example :
Given array arr = [12, 3, 0, 2, 8, 11, 0, 0, 6, 4, 0, 5, 7, 0, 8, 9, 0]
output: [12, 3, 2, 8, 11, 6, 4, 5, 7, 8, 9, 0, 0, 0, 0, 0, 0]

Solution

Top comments (6)

Brad • Sep 25 '19 • Edited

This is my "code-golf-esque" solution.

const arr = [12, 3, 0, 2, 8, 11, 0, 0, 6, 4, 0, 5, 7, 0, 8, 9, 0];

const combine = ({ nums, zeros }) => [...nums, ...zeros];
const moveZeroes = arr =>
  combine(
    arr.reduce(
      (acc, num) =>
        (num === 0 ? acc.zeros.push(num) : acc.nums.push(num)) && acc,
      {
        nums: [],
        zeros: []
      }
    )
  );

console.log(moveZeroes(arr));

I wasn't to sure about what the "naive brute force" is. My current solution should always run at 2n where n is the number of integers in the array, this assumes the combine method just iterates the two arrays together.

I'm 100% sure there is a 1n approach, where you iterate over the array only 1 time, but I personally hate working on arrays I'm iterating over.

edit I didn't see this was tagged as a Java problem, and the above is JavaScript, so it is what it is haha.

akbhairwal • Sep 25 '19

oh Sorry... I should make it language independent..
I think it can be done in single array iteration and having two pointer for swapping

Oleksii Filonenko • Sep 25 '19

Rust, my best shot at performance (checked with benchmarks):

pub fn move_zeros_to_end_deque(nums: &[i32]) -> VecDeque<i32> {
    let mut deque = VecDeque::with_capacity(nums.len());
    for &n in nums.into_iter().rev() {
        if n == 0 {
            deque.push_back(n);
        } else {
            deque.push_front(n);
        }
    }
    deque
}

Benserya • Sep 25 '19

did u try the given array in ur solution?

Gab • Sep 29 '19

O(n) Clojure solution:

(defn move-zeros [arr]
  (loop [lst arr 
         nonzeros []
         zeros []]
    (cond
      (empty? lst) (concat nonzeros zeros)
      (= (first lst) 0) (recur (rest lst) nonzeros (conj zeros 0))
      :else (recur (rest lst) (conj nonzeros (first lst)) zeros))))

(move-zeros [12 3 0 2 8 11 0 0 6 4 0 5 7 0 8 9 0])
;; (12 3 2 8 11 6 4 5 7 8 9 0 0 0 0 0 0)

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6-10PM challenge problem #001

Top comments (6)

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