LeetCode - First Missing Positive

First Missing Positive

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