Leetcode no. 41

41. First Missing Positive

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 Solution {
    public int firstMissingPositive(int[] nums) {
        if (nums.length==0) return 1;
        for (int i=0; i<nums.length; i++){
            while (nums[i]>0 && nums[i]<= nums.length && nums[i]!=i+1){
                if (nums[i]== nums[nums[i]-1]) break;
                int tmp= nums[nums[i]-1];
                nums[nums[i]-1]= nums[i];
                nums[i]= tmp;
            }
        }
        for (int i=0; i<nums.length; i++){
            if (nums[i]!=i+1) return i+1;
        }
        return nums[nums.length-1]+1;
    }
}