LeetCode 41.First Missing Positive

Given an unsorted integer array, find the smallest missing positive integer.

Example 1:

Input: [1,2,0]
Output: 3

Example 2:

Input: [3,4,-1,1]
Output: 2

Example 3:

Input: [7,8,9,11,12]
Output: 1

Note:

Your algorithm should run in O(n) time and uses constant extra space.

解答：

class Solution:
	def firstMissingPositive(self, nums):
		"""
		:type nums: List[int]
		:rtype: int
		"""
		i = 0
		length = len(nums)
		while i < length:
			if nums[i] == i + 1 or nums[i] > length or nums[i] <= 0:
				i += 1
			else:
				index = nums[i] - 1
				if nums[index] == nums[i]:
					i += 1
					continue

				nums[i], nums[index] = nums[index], nums[i]

		min = 1
		i = 0
		while i < length and nums[i] == i + 1 :
			i += 1

		return i + 1