题目：

题解：

func singleNonDuplicate(nums []int) int {
    low, high := 0, len(nums)-1
    for low < high {
        mid := low + (high-low)/2
        mid -= mid & 1
        if nums[mid] == nums[mid+1] {
            low = mid + 2
        } else {
            high = mid
        }
    }
    return nums[low]
}