# 324. Wiggle Sort II

### Problem:

Given an unsorted array nums, reorder it such that nums[0] < nums[1] > nums[2] < nums[3]....

Example: (1) Given nums = [1, 5, 1, 1, 6, 4], one possible answer is [1, 4, 1, 5, 1, 6]. (2) Given nums = [1, 3, 2, 2, 3, 1], one possible answer is [2, 3, 1, 3, 1, 2].

Note: You may assume all input has valid answer.

Follow Up: Can you do it in O(n) time and/or in-place with O(1) extra space?

### Solutions:

``````public class Solution {
public void wiggleSort(int[] nums) {
int[] tmp = new int[nums.length];
Arrays.sort(nums);
int left = (nums.length - 1) / 2, right = nums.length - 1;
for (int i = 0; i < tmp.length; i ++) {
if (i % 2 == 0) {
tmp[i] = nums[left--];
}
else {
tmp[i] = nums[right--];
}
}
for (int i = 0; i < tmp.length; i ++) {
nums[i] = tmp[i];
}
}
}
``````
``````public class Solution {
public void wiggleSort(int[] nums) {
int median = quickSelect(nums, 0, nums.length - 1, (nums.length + 1)/ 2);
int i = 0, j = 0, k = nums.length - 1;
while (i <= k) {
int it = index(i, nums.length), jt = index(j, nums.length), kt = index(k, nums.length);
if (nums[it] > median) {
int tmp = nums[it];
nums[it] = nums[jt];
nums[jt] = tmp;
i ++;
j ++;
}
else if (nums[it] < median) {
int tmp = nums[it];
nums[it] = nums[kt];
nums[kt] = tmp;
k --;
}
else {
i ++;
}
}
}
private int index(int i, int n) {
if (i < n /2) {
return i * 2 + 1;
}
else {
return (i - n / 2) * 2;
}
}
private int partition(int[] nums, int left, int right) {
int x = nums[right];
int i = left;
int j = right - 1;
while (i <= j) {
if (nums[i] <= x) {
i ++;
}
else {
if (nums[j] > x) {
j --;
}
else {
int tmp = nums[i];
nums[i] = nums[j];
nums[j] = tmp;
i ++;
j --;
}
}
}
nums[right] = nums[i];
nums[i] = x;
return i;
}
private int quickSelect(int[] nums, int left, int right, int i) {
if (left == right) {
return nums[left];
}
int q = partition(nums, left, right);
int k = q - left + 1;
if (i == k){
return nums[q];
}
else if (i < k) {
return quickSelect(nums, left, q - 1, i);
}
else {
return quickSelect(nums, q + 1, right, i - k);
}
}
}
``````