01天【代码随想录算法训练营34期】 第一章 数组part01 (704. 二分查找、 27. 移除元素)

704. 二分查找

• 先选是[low, high]还是[low, high)还是(low, high]

• 下面选择[]

• "while (low <= high)"还是"while (low < high)"
  因为[1,1]合法，所以是<=（什么是不合法呢，比如说[2,1]）

• "high = mid - 1"还是"high = mid"
  这个情况，我们已知nums[mid] > target，所以下一个区间不能包含mid，所以high = mid-1

class Solution(object):
    def search(self, nums, target):
        low = 0
        high = len(nums) - 1
        while (low <= high):
            mid = (high + low) // 2
            if nums[mid] == target:
                return mid
            elif nums[mid] > target:
                high = mid - 1
            else:
                low = mid + 1
        return -1

Complexity: O(log(n))

27. 移除元素
快慢指针

class Solution(object):
    def removeElement(self, nums, val):
        i = 0
        j = 0
        while j < len(nums):
            if (nums[j] != val):
                nums[i] = nums[j]
                i += 1
            j += 1
        return i

Complexity: O(n)