1664. Number of schemes to generate balance numbers One question daily

1664. Number of schemes to generate balance numbers

Thought：

See when you read the question medium I know that it is definitely not really going to delete an element。Otherwise it will time out，So I tried to try polepythonFeature code：Use slice to process all data；
But it’s timeout。。

然后看官方answer，用的Dynamic planning。中心Thought是：

General nature，Now we will settle down i Delete elements，
Obviously the bidding i The previous element bidding will not change from this，Bidding i
The original was originally j，j>iThe array elements of the bid will move to the bidding j−1，
Immediately bidding i The subsequent bidding elements will become the rated element，
The even bidding element will become a strange number of bidding elements。

Code

slice

class Solution:
    def waysToMakeFair(self, nums: List[int]) -> int:
        flag = 0
        for i in range(len(nums)):
            temp_nums = nums[:i] + nums[i+1:]
            if sum(temp_nums[::2])==sum(temp_nums[1::2]):
                flag += 1
        return flag

官方answer

class Solution:
    def waysToMakeFair(self, nums: List[int]) -> int:
        res = odd1 = even1 = odd2 = even2 = 0
        for i, num in enumerate(nums):
            if i & 1:
                odd2 += num
            else:
                even2 += num
        for i, num in enumerate(nums):
            if i & 1:
                odd2 -= num
            else:
                even2 -= num
            if odd1 + even2 == odd2 + even1:
                res += 1
            if i & 1:
                odd1 += num
            else:
                even1 += num
        return res