题解 | #三数之和#

class Solution {
  public:
    vector<vector<int> > threeSum(vector<int>& num) {
        vector<vector<int> > res;
        int n = num.size();
        //不够三元组
        if (n < 3)
            return res;
        //排序
        sort(num.begin(), num.end());
        for (int i = 0; i < n - 2; i++) {
            int target = -num[i];
            if (i != 0 && num[i] == num[i - 1]) {
                continue;
            }
            for (int j = i + 1; j < n - 1; j++) {
                if (j != i+1 && num[j] == num[j - 1]) {
                    continue;
                }
                for (int k = j + 1; k < n; k++) {
                    if (k != j+1 && num[k] == num[k - 1]) {
                        continue;
                    }
                    if (num[j] + num[k] == target) {
                        res.push_back({num[i], num[j], num[k]});
                    }
                }
            }
        }
        return res;
    }
};