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Update 0018.四数之和.md
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@ -207,35 +207,40 @@ class Solution {
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```
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Python:
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(版本一) 双指针
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```python
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# 双指针法
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class Solution:
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def fourSum(self, nums: List[int], target: int) -> List[List[int]]:
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def fourSum(self, nums: List[int], target: int) -> List[List[int]]:
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result = []
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nums.sort()
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n = len(nums)
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res = []
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for i in range(n):
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if i > 0 and nums[i] == nums[i - 1]: continue # 对nums[i]去重
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for k in range(i+1, n):
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if k > i + 1 and nums[k] == nums[k-1]: continue # 对nums[k]去重
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p = k + 1
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q = n - 1
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while p < q:
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if nums[i] + nums[k] + nums[p] + nums[q] > target: q -= 1
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elif nums[i] + nums[k] + nums[p] + nums[q] < target: p += 1
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for k in range(len(nums)):
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if nums[k] > target and nums[k] >= 0:
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break
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if k > 0 and nums[k] == nums[k-1]:
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continue
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for i in range(k+1, len(nums)):
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if nums[k] + nums[i] > target and nums[k] + nums[i] >= 0:
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break
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if i > k+1 and nums[i] == nums[i-1]:
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continue
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left, right = i+1, len(nums)-1
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while right > left:
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if nums[k] + nums[i] + nums[left] + nums[right] > target:
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right -= 1
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elif nums[k] + nums[i] + nums[left] + nums[right] < target:
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left += 1
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else:
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res.append([nums[i], nums[k], nums[p], nums[q]])
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# 对nums[p]和nums[q]去重
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while p < q and nums[p] == nums[p + 1]: p += 1
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while p < q and nums[q] == nums[q - 1]: q -= 1
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p += 1
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q -= 1
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return res
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result.append([nums[k], nums[i], nums[left], nums[right]])
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while right > left and nums[right] == nums[right-1]:
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right -= 1
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while right > left and nums[left] == nums[left+1]:
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left += 1
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right -= 1
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left += 1
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return result
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```
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(版本二) 使用字典
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```python
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# 哈希表法
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class Solution(object):
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def fourSum(self, nums, target):
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"""
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