41. First Missing Positive

class Solution {
    public int firstMissingPositive(int[] nums) {
        int i = 0;
        while(i<nums.length){
            // switch the number at position i and nums[i]-1
            // i.e. move the number at i to nums[i]-1;
            if(nums[i]>0 && nums[i] <= nums.length && nums[i]!=nums[nums[i]-1]){
                int temp = nums[i];
                nums[i] = nums[nums[i]-1];
                nums[temp-1] = temp;
            }else{
                i++;
            }
        }
        
        for (int j = 0; j<nums.length; j++){
            if(j+1 != nums[j]){
                return j+1;
            }
        }
        // if no number missing until the largest number in the array
        return i+1;
    }
}