重新排序一个序列



问题：

给定一个序列，按照num[0]<num[1]>num[2]<num[3].........

样例： Given nums = [1, 5, 1, 1, 6, 4], one possible answer is [1, 4, 1, 5, 1, 6].

解决方案：

void wiggleSort(vector<int>& nums) {
if (nums.empty()) {
return;
}   
int n = nums.size();

// Step 1: Find the median
vector<int>::iterator nth = next(nums.begin(), n / 2);
nth_element(nums.begin(), nth, nums.end());
int median = *nth;

// Step 2: Tripartie partition within O(n)-time & O(1)-space.
auto m = [n](int idx) { return (2 * idx + 1) % (n | 1); };   
int first = 0, mid = 0, last = n - 1;
while (mid <= last) {
if (nums[m(mid)] > median) {
swap(nums[m(first)], nums[m(mid)]);
++first;
++mid;
}
else if (nums[m(mid)] < median) {
swap(nums[m(mid)], nums[m(last)]);
--last;
}
else {
++mid;
}
}
}