class Solution {
    public int singleNonDuplicate(int[] nums) {
        int low = 0, high = nums.length-1;
        
        while(low <high)
        {
            int mid = (high+low)/2; //watchout
            
            if(mid%2 == 1)
                mid --;
            
            if(nums[mid] != nums[mid+1]) 
                high = mid;
            else
                low = mid+2;
        }
        return nums[low];
    }
}