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15_3sum.cpp
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15_3sum.cpp
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//Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.
//
//Note:
//
//Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ¡ b ¡ c)
//The solution set must not contain duplicate triplets.
//
// For example, given array S = {-1 0 1 2 -1 -4},
//
// A solution set is:
// (-1, 0, 1)
// (-1, -1, 2)
//
class Solution {
public:
vector<vector<int>> threeSum(vector<int>& nums)
{
vector<vector<int>>result;
if ( 0 == nums.size())
{
return result;
}
sort(nums.begin(), nums.end());
int n = nums.size();
for ( int i = 0; i < n -2; i++)
{
if ( i > 0 && nums[i] == nums[i-1])
{
continue;
}
int firstelement = nums[i];
int start = i+1, end = n-1;
while ( start < end)
{
if (nums[start]+nums[end]+ firstelement == 0)
{
vector<int>set;
set.push_back(nums[i]);
set.push_back(nums[start]);
set.push_back(nums[end]);
sort(set.begin(), set.end());
result.push_back(set);
start++;
end--;
while( start < end && nums[end] == nums[end+1])
{
end--;
}
while( start < end && nums[start] == nums[start-1])
{
start++;
}
}
else if (nums[start]+nums[end]+ firstelement > 0)
{
end--;
while( start < end && nums[end] == nums[end+1])
{
end--;
}
}
else
{
start++;
while( start < end && nums[start] == nums[start-1])
{
start++;
}
}
}
}
return result;
}
};