Leetcode 刷题笔记1 贪心算法part02

leetcode 122 买股票的最佳时机||

简单题

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        result = 0
        for i in range(1, len(prices)):
            profit = prices[i] - prices[i - 1]
            result += max(profit, 0)
        return result

leetcode 55 跳跃游戏

初步理解贪心是对遍历的剪枝

class Solution:
    def canJump(self, nums: List[int]) -> bool:
        cover = 0
        if len(nums) < 2 : return True
        for i in range(len(nums)):
            if i <= cover:
                cover = max(i + nums[i], cover)
            if cover >= len(nums) - 1:
                return True
        return False

leetcode 45 跳跃游戏||

好难 摸不到规律

class Solution:
    def jump(self, nums: List[int]) -> int:
        if len(nums) == 1:
            return 0
        cur_distance, next_ditance, ans = 0, 0, 0
        for i in range(len(nums)):
            next_ditance = max(next_ditance, nums[i] + i)
            if i == cur_distance:
                cur_distance = next_ditance
                ans += 1
                if next_ditance >= len(nums) - 1:
                    break
        return ans

leetcode 1005 k次取反后最大化的数组和

class Solution:
    def largestSumAfterKNegations(self, nums: List[int], k: int) -> int:
        nums.sort(key = lambda x: abs(x), reverse = True)
        for i in range(len(nums)):
            if nums[i] < 0 and k > 0:
                nums[i] *= -1
                k -= 1
        if k % 2 == 1:
            nums[-1] *= -1
        return sum(nums)

关于贪心算法，从上述题目中并没有体会到其特殊之处，对它的初步印象还是暴力解法的优化