LeetCode 41.First Missing Positive

最新推荐文章于 2024-06-04 16:28:00 发布

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本文介绍了一种在未排序整数数组中寻找最小缺失正整数的方法，该算法需在O(n)时间内运行并使用常数级额外空间。通过一系列示例展示了如何通过调整数组元素位置来找到缺失的正整数。

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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