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.
难点:需要O(n)的时间复杂度且需要常数空间。
AC代码:
class Solution(object): def firstMissingPositive(self, nums): """ :type nums: List[int] :rtype: int """ L=len(nums) for m in range(L): if nums[m]>L: continue val = nums[m]-1 while nums[m]>0 and val<L and nums[val] != nums[m]: #小于等于0,大于等于长度的不换。 nums[m],nums[val]=nums[val],nums[m] val = nums[m]-1 for m in range(len(nums)): if nums[m] != m +1: return m +1 return L+1