# 数组
## 二分
```python
def binary_search(nums, target):
    left, right = 0, len(nums) - 1
    while left <= right:
        mid = left + (right - left) // 2  # 防止溢出
        if nums[mid] == target:
            return mid  # 找到目标，返回索引
        elif nums[mid] < target:
            left = mid + 1  # 目标在右半部分
        else:
            right = mid - 1  # 目标在左半部分
    return -1  # 未找到目标

# 左右边界
def left_bound(nums, target):
    left, right = 0, len(nums) - 1
    while left <= right:
        mid = left + (right - left) // 2
        if nums[mid] < target:
            left = mid + 1
        else:
            right = mid - 1
    return left if left < len(nums) and nums[left] == target else -1
def right_bound(nums, target):
    left, right = 0, len(nums) - 1
    while left <= right:
        mid = left + (right - left) // 2
        if nums[mid] <= target:
            left = mid + 1
        else:
            right = mid - 1
    return right if right >= 0 and nums[right] == target else -1

```