[LintCode] 3Sum 三数之和

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.

Notice

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.

Have you met this question in a real interview?

Yes

Example

For example, given array S = {-1 0 1 2 -1 -4}, A solution set is:

(-1, 0, 1)
(-1, -1, 2)

LeetCode上的原题，请参见我之前的博客3Sum。

class Solution {
public:
    /**
     * @param numbers : Give an array numbers of n integer
     * @return : Find all unique triplets in the array which gives the sum of zero.
     */
    vector<vector<int> > threeSum(vector<int> &nums) {
        vector<vector<int>> res;
        sort(nums.begin(), nums.end());
        for (int k = ; k < nums.size() - ; ++k) {
            if (nums[k] > ) break;
            if (k >  && nums[k] == nums[k - ]) continue;
            int target =  - nums[k], i = k + , j = nums.size() - ;
            while (i < j) {
                if (nums[i] + nums[j] == target) {
                    res.push_back({nums[k], nums[i], nums[j]});
                    while (i < j && nums[i] == nums[i + ]) ++i;
                    while (i < j && nums[j] == nums[j - ]) --j;
                    ++i; --j;
                } else if (nums[i] + nums[j] < target) ++i;
                else --j;
            }
        }
        return res;
    }
};