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feat: add python and java solutions to lcof question
添加《剑指 Offer》题解:面试题51. 数组中的逆序对
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name: Sync | ||
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on: | ||
push: | ||
branches: [ master ] | ||
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jobs: | ||
build: | ||
runs-on: ubuntu-latest | ||
steps: | ||
- name: Sync to Gitee | ||
uses: wearerequired/git-mirror-action@master | ||
env: | ||
SSH_PRIVATE_KEY: ${{ secrets.GITEE_RSA_PRIVATE_KEY }} | ||
with: | ||
source-repo: "[email protected]:doocs/leetcode.git" | ||
destination-repo: "[email protected]:Doocs/leetcode.git" |
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# [面试题51. 数组中的逆序对](https://leetcode-cn.com/problems/shu-zu-zhong-de-ni-xu-dui-lcof/) | ||
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## 题目描述 | ||
<!-- 这里写题目描述 --> | ||
在数组中的两个数字,如果前面一个数字大于后面的数字,则这两个数字组成一个逆序对。输入一个数组,求出这个数组中的逆序对的总数。 | ||
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**示例 1:** | ||
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``` | ||
输入: [7,5,6,4] | ||
输出: 5 | ||
``` | ||
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**限制:** | ||
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- `0 <= 数组长度 <= 50000` | ||
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## 解法 | ||
<!-- 这里可写通用的实现逻辑 --> | ||
在归并中统计逆序对。 | ||
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### Python3 | ||
<!-- 这里可写当前语言的特殊实现逻辑 --> | ||
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```python | ||
class Solution: | ||
def reversePairs(self, nums: List[int]) -> int: | ||
self.res = 0 | ||
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def merge(part1, part2, nums): | ||
len1, len2 = len(part1) - 1, len(part2) - 1 | ||
t = len(nums) - 1 | ||
while len1 >= 0 and len2 >= 0: | ||
if part1[len1] > part2[len2]: | ||
self.res += (len2 + 1) | ||
nums[t] = part1[len1] | ||
len1 -= 1 | ||
else: | ||
nums[t] = part2[len2] | ||
len2 -= 1 | ||
t -= 1 | ||
while len1 >= 0: | ||
nums[t] = part1[len1] | ||
t -= 1 | ||
len1 -= 1 | ||
while len2 >= 0: | ||
nums[t] = part2[len2] | ||
t -= 1 | ||
len2 -= 1 | ||
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def merge_sort(nums): | ||
if len(nums) < 2: | ||
return | ||
mid = len(nums) // 2 | ||
s1, s2 = nums[:mid], nums[mid:] | ||
merge_sort(s1) | ||
merge_sort(s2) | ||
merge(s1, s2, nums) | ||
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merge_sort(nums) | ||
return self.res | ||
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``` | ||
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### Java | ||
<!-- 这里可写当前语言的特殊实现逻辑 --> | ||
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```java | ||
class Solution { | ||
private int res = 0; | ||
public int reversePairs(int[] nums) { | ||
int n = nums.length; | ||
if (n < 2) { | ||
return 0; | ||
} | ||
mergeSort(nums, 0, n - 1); | ||
return res; | ||
} | ||
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private void mergeSort(int[] nums, int s, int e) { | ||
if (s == e) { | ||
return; | ||
} | ||
int mid = s + ((e - s) >> 1); | ||
mergeSort(nums, s, mid); | ||
mergeSort(nums, mid + 1, e); | ||
merge(nums, s, mid, e); | ||
} | ||
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private void merge(int[] nums, int s, int mid, int e) { | ||
int n = e - s + 1; | ||
int[] help = new int[n]; | ||
int i = s, j = mid + 1, idx = 0; | ||
while (i <= mid && j <= e) { | ||
if (nums[i] > nums[j]) { | ||
res += (mid - i + 1); | ||
help[idx++] = nums[j++]; | ||
} else { | ||
help[idx++] = nums[i++]; | ||
} | ||
} | ||
while (i <= mid) { | ||
help[idx++] = nums[i++]; | ||
} | ||
while (j <= e) { | ||
help[idx++] = nums[j++]; | ||
} | ||
for (int t = 0; t < n; ++t) { | ||
nums[s + t] = help[t]; | ||
} | ||
} | ||
} | ||
``` | ||
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### ... | ||
``` | ||
``` |
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class Solution { | ||
private int res = 0; | ||
public int reversePairs(int[] nums) { | ||
int n = nums.length; | ||
if (n < 2) { | ||
return 0; | ||
} | ||
mergeSort(nums, 0, n - 1); | ||
return res; | ||
} | ||
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private void mergeSort(int[] nums, int s, int e) { | ||
if (s == e) { | ||
return; | ||
} | ||
int mid = s + ((e - s) >> 1); | ||
mergeSort(nums, s, mid); | ||
mergeSort(nums, mid + 1, e); | ||
merge(nums, s, mid, e); | ||
} | ||
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private void merge(int[] nums, int s, int mid, int e) { | ||
int n = e - s + 1; | ||
int[] help = new int[n]; | ||
int i = s, j = mid + 1, idx = 0; | ||
while (i <= mid && j <= e) { | ||
if (nums[i] > nums[j]) { | ||
res += (mid - i + 1); | ||
help[idx++] = nums[j++]; | ||
} else { | ||
help[idx++] = nums[i++]; | ||
} | ||
} | ||
while (i <= mid) { | ||
help[idx++] = nums[i++]; | ||
} | ||
while (j <= e) { | ||
help[idx++] = nums[j++]; | ||
} | ||
for (int t = 0; t < n; ++t) { | ||
nums[s + t] = help[t]; | ||
} | ||
} | ||
} |
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class Solution: | ||
def reversePairs(self, nums: List[int]) -> int: | ||
self.res = 0 | ||
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def merge(part1, part2, nums): | ||
len1, len2 = len(part1) - 1, len(part2) - 1 | ||
t = len(nums) - 1 | ||
while len1 >= 0 and len2 >= 0: | ||
if part1[len1] > part2[len2]: | ||
self.res += (len2 + 1) | ||
nums[t] = part1[len1] | ||
len1 -= 1 | ||
else: | ||
nums[t] = part2[len2] | ||
len2 -= 1 | ||
t -= 1 | ||
while len1 >= 0: | ||
nums[t] = part1[len1] | ||
t -= 1 | ||
len1 -= 1 | ||
while len2 >= 0: | ||
nums[t] = part2[len2] | ||
t -= 1 | ||
len2 -= 1 | ||
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def merge_sort(nums): | ||
if len(nums) < 2: | ||
return | ||
mid = len(nums) // 2 | ||
s1, s2 = nums[:mid], nums[mid:] | ||
merge_sort(s1) | ||
merge_sort(s2) | ||
merge(s1, s2, nums) | ||
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merge_sort(nums) | ||
return self.res |