def find_median(nums): n = len(nums) if n == 0: return None def quick_select(nums, l, r, k): if l == r: return nums[l] pivot = nums[r] i = l for j in range(l, r): if nums[j] <= pivot: nums[i], nums[j] = nums[j], nums[i] i += 1 nums[i], nums[r] = nums[r], nums[i] if k == i: return nums[k] elif k < i: return quick_select(nums, l, i-1, k) else: return quick_select(nums, i+1, r, k) if n % 2 == 1: return quick_select(nums, 0, n-1, n//2) else: left = quick_select(nums, 0, n-1, n//2-1) right = quick_select(nums, 0, n-1, n//2) return (left + right) / 2