15_3sum.cc

#include <vector>
#include <algorithm>
 
using Vec = std::vector<int>;
using VecVec = std::vector<Vec>;
using std::sort;
 
class Solution {
public:
    VecVec threeSum(Vec& nums) {
        sort(nums.begin(), nums.end());
        VecVec result;
 
        for (int i = 0; i < nums.size(); i++) {
            // no duplicate
            if (i > 0 && nums[i - 1] == nums[i]) continue;
 
            int left = i + 1;
            int right = nums.size() - 1;
 
            while (left < right) {
                int sum = nums[i] + nums[left] + nums[right];
                
                if (sum < 0) {
                    ++left;
                } else if (sum > 0) {
                    --right;
                } else {
                    result.push_back({nums[i], nums[left], nums[right]});
 
                    // No dup
                    while (left < right && nums[left] ==  nums[left + 1]) ++left;
                    while (left < right && nums[right] == nums[right - 1]) --right;
 
                    ++left;
                    --right;
                }
            }
        }
 
        return result;
    }
};