Given an unsorted integer array, find the first missing positive integer.

/*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.*/
public class FindFirstLostPositive {

public static void main(String[] args) {
System.out.println(new FindFirstLostPositive().firstMissingPositive(new int[]{-1,-2,-3,1,2,3,4,5,6,7,8,9}));
}
public int firstMissingPositive(int[] nums) {

if(nums.length==0||nums==null)
return 1;
//1放在nums[0]，2放在nums[1]
for(int i = 0;i<nums.length;i++)
{
while(nums[i]!=i+1)
{
if(nums[i]>=nums.length||nums[i]<=0||nums[i]==nums[nums[i]-1])
break;
int temp = nums[i];
nums[i] = nums[temp-1];
nums[temp-1] = temp;
}
}

for(int i = 0;i<nums.length;i++)
{
if(nums[i]!=i+1)
return i+1;
}
return nums.length+1;
}
}