[閒聊] Leetcode Weekly Contest 407

[dont (dont)]

第一題
Number of Bit Changes to Make Two Integers Equal

## 思路

掃32bit,
如果k的bit為0,n的bit為1 回傳-1
如果k的bit為1,n的bit為0 change+1

## Code

```python
class Solution:
    def minChanges(self, n: int, k: int) -> int:
        ans = 0
        for i in range(32):
            if n & 1 and k & 1 == 0:
                ans += 1
            if n & 1 == 0 and k & 1:
                return -1

            n >>= 1
            k >>= 1
        return ans
```

第二題
Vowels Game in a String

## 思路

計算vowels數量,

奇數個 - Alice直接獲勝
偶數個 - 刪掉奇數個vowels會剩下三種Case: bab / ba / a, 也都會是Alice獲勝

所以只有零個的時候會是False

## Code

```python
class Solution:
    def doesAliceWin(self, s: str) -> bool:
        vowels = {'a', 'e', 'i', 'o', 'u'}

        count = 0
        for ch in s:
            if ch in vowels:
                count += 1

        if count == 0:
            return False
        return True
```

第三題
Maximum Number of Operations to Move Ones to the End

## 思路

由左往右掃, 紀錄1的個數ones
每次遇到0的時候就移動ones個1 (重複0時略過)

## Code

```python
class Solution:
    def maxOperations(self, s: str) -> int:
        n = len(s)

        ans = ones = 0
        i = 0
        for i in range(n):
            if i and s[i] == s[i-1] == '0':
                continue
            if s[i] == '0':
                ans += ones
            else:
                ones += 1
        return ans
```

第四題
Minimum Operations to Make Array Equal to Target

## 思路

如果 diff[1:3] > 0 而 diff[3] <= 0 的時候
只會對nums[1:3] 做Increment, 對nums[3:??] 做Decrement

在nums[1:3]範圍內就是加上diff差值

## Code

```python
class Solution:
    def minimumOperations(self, nums: List[int], target: List[int]) -> int:
        n = len(nums)
        diff = [n-t for n, t in zip(nums, target)]

        ans = abs(diff[0])
        for i in range(1, n):
            if diff[i] * diff[i-1] <= 0:
                ans += abs(diff[i])
            else:
                ans += max(abs(diff[i]) - abs(diff[i-1]), 0)

        return ans
```

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