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].

此题需要把数组序号分成偶数和奇数来区别对待，代码如下：

public class Solution {
    public void wiggleSort(int[] nums) {
        for(int i=0;i<nums.length;i++){
            // the index is even
            if(i%2==0){
                if(i+1<nums.length&&nums[i]>nums[i+1]){
                    swap(nums,i,i+1);
                }
            }else{
            // the index is odd
                if(i+1<nums.length&&nums[i]<nums[i+1]){
                    swap(nums,i,i+1);
                }
            }
        }
    }
    public void swap(int[] nums,int i,int j){
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }
}
// run time complexity is O(n),the space complexity is O(1);