func duplicateInArray(nums []int) int {
l := 1
r := len(nums) - 1
for l < r {
mid := l + (r - l) >> 1
count := 0
for _, num := range nums {
if num >= l && num <= mid {
count ++
}
}
if count > mid - l + 1 {
r = mid
} else {
l = mid + 1
}
}
return r
}