question
Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.
Note:
The solution set must not contain duplicate triplets.
Example:
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Given array nums = [-1, 0, 1, 2, -1, -4], |
Solution
method 1
-
三重循环暴力解决，排序用来去重(bug)
-
使用unique去重
nums.erase(unique(nums.begin(),nums.end()),nums.end());1
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using namespace std;
static const int accelerate = []() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
return 0;
}();
class {
public:
vector<vector<int>> threeSum(vector<int>& nums) {
vector<vector<int>> result;
int length = nums.size();
if (length < 3)
{
return result;
}
sort(nums.begin(), nums.end());
for (int i = 0; i < length - 2; i++)
{
for (int j = i + 1; j < length - 1; j++)
{
for (int k = j + 1; k < length; k++)
{
if (nums[i] + nums[j] == -nums[k]&&nums[i] !=nums[i-1])
result.push_back({ nums[i], nums[j], nums[k] });
}
}
}
return result;
}
};
int main(void)
{
vector<int> nums = { -1, 0, 1, 2, -1, -4 };
vector<vector<int>> result;
Solution s;
result=s.threeSum(nums);
return 0;
}
method 2
-
双指针
-
去重通过缩小区间（忽略和使用的元素相等的元素来实现）
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using namespace std;
static const int accelerate = []() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
return 0;
}();
class {
public:
vector<vector<int> > threeSum(vector<int>& nums) {
int length = nums.size();
if (length <= 2) return {};
vector<vector<int> > triple;
sort(nums.begin(), nums.end());
for (int i = 0; i < length;) {
int start = i + 1, end = length - 1;
while (start < end) {
if (nums[i] + nums[start] + nums[end] == 0) {
triple.push_back({ nums[i],nums[start],nums[end] });
start++;
end--;
while ((start < end) && nums[start] == nums[start - 1]) start++;
while ((start < end) && nums[end] == nums[end + 1]) end--;
}
else if (nums[i] + nums[start] + nums[end] < 0) {
start++;
while ((start < end) && nums[start] == nums[start - 1]) start++;
}
else {
end--;
while ((start < end) && nums[end] == nums[end + 1]) end--;
}
}
i++;
while ((i < length) && nums[i] == nums[i - 1])
i++;
}
return triple;
}
};
int main(void)
{
vector<int> nums = { -1,0,1,2,-1,-4};
vector<vector<int>> triple;
Solution s;
triple=s.threeSum(nums);
return 0;
}
to be continued
2019年4月6日 18点56分
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