3Sum

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Given an array S of n integers, are there elements abc 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> &num) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        vector<vector<int> > result;        set<vector<int> > record;        if (num.size() < 3) {            return result;        }        sort(num.begin(), num.end());        vector<int> got;        int sum = 0;        for (int i = 0; i < num.size() - 2; ++i) {            int low = i + 1;            int high = num.size() - 1;            while (low < high) {                sum = num[i] + num[low] + num[high];                if (sum == 0) {                    got.push_back(num[i]);                    got.push_back(num[low]);                    got.push_back(num[high]);                    if (record.find(got) == record.end()) {                        record.insert(got);                        result.push_back(got);                    }                    got.clear();                    --high;                } else if (sum > 0) {                    --high;                } else {                    ++low;                }            }        }        return result;    }};


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