Given an unsorted integer array, find the first missing positive integer.
For example,
Given [1,2,0]
return 3
,
and [3,4,-1,1]
return 2
.
Your algorithm should run in O(n) time and uses constant space.
在leetcode里发现了这道题目。很巧妙地把A[i]和A[A[i]-1]交换,使得原先A[A[i]-1]的位置上存放正确的对应数值。最后从前往后遍历找出第一个不符合的。好巧妙啊