注意全部是闭区间搜索
1. 基础
left = 0
right = len(nums)-1 #[left, right]闭区间
while left <= right:
mid = left + (right - left) // 2
if nums[mid] == target:
return mid
elif nums[mid] < target:
left = mid + 1
elif nums[mid] > target:
right = mid - 1
return -1 # while终止时 left>right仍然没找到 返回-1
2. 寻找左侧边界
left = 0
right = len(nums)-1
while left <= right:
mid = left + (right - left) // 2
if nums[mid] == target:
right = mid - 1
elif nums[mid] < target:
left = mid + 1
elif nums[mid] > target:
right = mid - 1
if left>=len(nums) or nums[left]!=target:
return -1 # 越界
return left
3. 寻找右侧边界
left = 0
right = len(nums)-1
while left <= right:
mid = left + (right - left) // 2
if nums[mid] == target:
left = mid + 1
elif nums[mid] < target:
left = mid + 1
elif nums[mid] > target:
right = mid - 1
if right<0 or nums[right]!=target:
return -1 # 越界
return right
