Problem: 704. 二分查找

坑点

  1. r = len(nums) - 1 忘记写 -1了
  2. while l <= r: 这里需要等于，这样l == r的时候，可以计算一下当前的mid再多走一步

代码

普通二分查找

class Solution(object):
    def search(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: int
        """
        l = 0
        r = len(nums) - 1
        while l <= r:
            mid = (l + r) // 2
            if nums[mid] < target:
                l = mid + 1
            elif nums[mid] > target:
                r = mid - 1
            else:
                return mid
        return -1

二分找上限

class Solution(object):
    def search(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: int
        """
        l = 0
        r = len(nums) - 1
        while l <= r:
            mid = (l + r) // 2
            if nums[mid] <= target:
                l = mid + 1
            else:
                r = mid - 1
        return l - 1 if nums[l - 1] == target else -1