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Update 0018.四数之和.md

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jianghongcheng
2023-05-05 21:36:38 -05:00
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problems/0018.四数之和.md
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@ -209,34 +209,38 @@ class Solution {
Python： Python：
(版本一) 双指针 (版本一) 双指针
```python ```python
def fourSum(self, nums: List[int], target: int) -> List[List[int]]: class Solution:
result = [] def fourSum(self, nums: List[int], target: int) -> List[List[int]]:
nums.sort() nums.sort()
for k in range(len(nums)): n = len(nums)
if nums[k] > target and nums[k] >= 0: result = []
for i in range(n):
if nums[i] > target and nums[i] > 0 and target > 0:# 剪枝（可省）
break break
if k > 0 and nums[k] == nums[k-1]: if i > 0 and nums[i] == nums[i-1]:# 去重
continue continue
for i in range(k+1, len(nums)): for j in range(i+1, n):
if nums[k] + nums[i] > target and nums[k] + nums[i] >= 0: if nums[i] + nums[j] > target and target > 0: #剪枝（可省）
break break
if i > k+1 and nums[i] == nums[i-1]: if j > i+1 and nums[j] == nums[j-1]: # 去重
continue continue
left, right = i+1, len(nums)-1 left, right = j+1, n-1
while right > left: while left < right:
if nums[k] + nums[i] + nums[left] + nums[right] > target: s = nums[i] + nums[j] + nums[left] + nums[right]
if s == target:
result.append([nums[i], nums[j], nums[left], nums[right]])
while left < right and nums[left] == nums[left+1]:
left += 1
while left < right and nums[right] == nums[right-1]:
right -= 1
left += 1
right -= 1 right -= 1
elif nums[k] + nums[i] + nums[left] + nums[right] < target: elif s < target:
left += 1 left += 1
else: else:
result.append([nums[k], nums[i], nums[left], nums[right]])
while right > left and nums[right] == nums[right-1]:
right -= 1
while right > left and nums[left] == nums[left+1]:
left += 1
right -= 1 right -= 1
left += 1
return result return result
``` ```
(版本二) 使用字典 (版本二) 使用字典