Monday, September 14, 2015

Leetcode: Wiggle Sort

Given an unsorted array nums, reorder it in-place such that nums[0] <= nums[1] >= nums[2] <= nums[3]....
For example, given nums = [3, 5, 2, 1, 6, 4], one possible answer is [1, 6, 2, 5, 3, 4].

Understand the problem:

A[0] <= A[1] >= A[2] <= A[3] >= A[4] <= A[5]
So we could actually observe that there is pattern that
A[even] <= A[odd],
A[odd] >= A[even].

Therefore we could go through the array and check this condition does not hold, just swap.

Code (Java):
public class Solution {
    public void wiggleSort(int[] nums) {
        if (nums == null || nums.length <= 1) {
            return;
        }
        
        for (int i = 0; i < nums.length - 1; i++) {
            if (i % 2 == 0) {
                if (nums[i] > nums[i + 1]) {
                    swap(nums, i, i + 1);
                }
            } else {
                if (nums[i] < nums[i + 1]) {
                    swap(nums, i, i + 1);
                }
            }
        }
    }
    
    private void swap(int[] nums, int i, int j) {
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }
}


4 comments:

  1. code fails for this input : int[] nums = {3,3,1,5,4};

    ReplyDelete
  2. Doesn't work for 1,1,3,3,2,2
    Gives 1 3 1 3 2 2
    A correct solution could have been 1 2 1 3 2 3

    ReplyDelete
  3. Here Question is modified as question includes the sign of equality where as original qustion does not !!!

    ReplyDelete