LeetCode First Missing Positive
2017-08-17 12:52
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LeetCode解题之First Missing Positive
原题
找出一个无序数组中缺少的最小的正整数。注意点:
时间复杂度为O(n)
仅仅能使用常数级额外空间
样例:
输入: nums = [1, 2, 0]
输出: 3
输入: nums = [3,4,-1,1]
输出: 2
解题思路
因为仅仅须要找出缺少的第一个正整数,我们最好还是把全部正数放到相应的位置。再找到第一个位置不匹配的地方原本应该放哪个数。如上面的样例[1,2,0]就已经排列好了,而[3,4,-1,1]应变为[1,-1,3,4]。分别遍历这两个数组,找到nums[i]!=i+1的位置,假设全部位置都符合,说明全部的数组成了从1開始的连续正整数。
进行排列的方法就是依次遍历每一个数字,把它们放到应该放置的位子。
AC源代码
class Solution(object): def firstMissingPositive(self, nums): """ :type nums: List[int] :rtype: int """ if not nums: return 1 i = 0 length = len(nums) while i < length: current = nums[i] if current <= 0 or current > length or nums[current - 1] == current: i += 1 else: nums[current - 1], nums[i] = nums[i], nums[current - 1] for i in range(length): if nums[i] != i + 1: return i + 1 return length + 1 if __name__ == "__main__": assert Solution().firstMissingPositive([1, 2, 0]) == 3 assert Solution().firstMissingPositive([1, 2, 3]) == 4 assert Solution().firstMissingPositive([3, 4, -1, 1]) == 2
欢迎查看我的Github (https://github.com/gavinfish/LeetCode-Python) 来获得相关源代码。
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