代码随想训练营第三十四天（Python）｜ 1005.K次取反后最大化的数组和、134. 加油站、135. 分发糖果

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)

134. 加油站
1、暴力法

class Solution:
    def canCompleteCircuit(self, gas: List[int], cost: List[int]) -> int:
        for i in range(len(gas)):
            rest = gas[i] - cost[i] # 剩余汽油量
            index = (i + 1) % len(gas) # 到达第几个加油站

            # 从第 i 个汽油站出发
            while rest > 0 and index != i:
                rest += gas[index] - cost[index]
                index = (index + 1) % len(gas)

            # 跑完一圈且汽油量大于等于0:
            if rest >= 0 and index == i:
                return i
        return -1

2、贪心法

class Solution:
    def canCompleteCircuit(self, gas: List[int], cost: List[int]) -> int:
        cur_gas = 0
        total_gas = 0
        start = 0

        for i in range(len(gas)):
            cur_gas += gas[i] - cost[i]
            total_gas += gas[i] - cost[i]

            if cur_gas < 0:
                start = i + 1
                cur_gas = 0
        if total_gas < 0:
            return -1

        return start

135. 分发糖果

class Solution:
    def candy(self, ratings: List[int]) -> int:
        n = len(ratings)
        res = [1] * n

        # 从左到右遍历
        for i in range(1, n):
            if ratings[i] > ratings[i-1]:
                res[i] = res[i-1] + 1

        # 从右到左遍历
        for j in range(n-2, -1, -1):
            if ratings[j] > ratings[j+1]:
                res[j] = max(res[j], res[j+1] + 1)

        return sum(res)