search_range.go

func searchRange(nums []int, target int) []int {
    // empty nums case
    if len(nums) == 0 {
        return []int{-1, -1}
    }
    // find starting and ending
    return []int{findStarting(nums, target), findEnding(nums, target)}
}

func findStarting(nums []int, target int) int {
    // binary search from 0 to len(nums) - 1
    lo := 0
    hi := len(nums) - 1

    for lo <= hi {
        mid := (lo + hi) / 2
        // < gets starting bound
        if nums[mid] < target {
            // too low, set lo to mid
            lo = mid + 1
        } else {
            // too high, set hi to mid
            hi = mid - 1
        }
    }
    // check lo valid
    if lo >= 0 && lo < len(nums) && nums[lo] == target {
        return lo
    }
    return -1
}

func findEnding(nums []int, target int) int {
    lo := 0
    hi := len(nums) - 1

    for lo <= hi {
        mid := (lo + hi) / 2
        // <= gets ending bound
        if nums[mid] <= target {
            lo = mid + 1
        } else {
            hi = mid - 1
        }
    }
    // check hi valid
    if hi >= 0 && hi < len(nums) && nums[hi] == target {
        return hi
    }
    return -1
}