【leetcode】41. first missing positive

public static int (int[] nums) {
    int i = 0;
    while(i < nums.length){
        if(nums[i] >= 1 && nums[i] <= nums.length && nums[nums[i]-1] != nums[i]) {
            swap(nums, i, nums[i]-1);
        }else{
            i++;
        }
    }
    i = 0;
    while(i < nums.length && nums[i] == i+1) 
        i++;
    return i+1;
}

private static void swap(int[] nums, int i, int j){
    int temp = nums[i];
    nums[i] = nums[j];
    nums[j] = temp;
}