280. 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].

一刷
题解：一个特别简单的思路，如果index为奇数，且小于左边，交换；
如果如果index为偶数，且大于左边，交换。

public class Solution {
    public void wiggleSort(int[] nums) {
        if(nums.length<=1) return;
        for(int i=1; i<nums.length; i++){
            if(i%2 == 1 && nums[i] < nums[i-1]) swap(nums, i, i-1);
            else if(i%2 == 0 && 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;
    }
}

二刷
用bit operation来提速

public class Solution {
    public void wiggleSort(int[] nums) {
        for (int i = 1; i < nums.length; i++)
            if (((i & 1) == 0) == (nums[i - 1] < nums[i])) xwap(nums, i);
    }

    private void xwap(int[] a, int i) {
        int t = a[i]; a[i] = a[i - 1]; a[i - 1] = t;
    }
}

三刷
同上