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.

题意：

给定无序数组，找出第一个未出现的正整数。

Solution1:

code