leetcode——15——3Sum

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> > ret;        int size = nums.size();        sort(nums.begin(), nums.end());        for(int i = 0; i < size; i ++)        {            //skip same i            while(i > 0 && i < size && nums[i] == nums[i-1])                i ++;            int j = i + 1;            int k = size - 1;            while(j < k)            {                int sum = nums[i] + nums[j] + nums[k];                if(sum == 0)                {                    vector<int> cur(3);                    cur[0] = nums[i];                    cur[1] = nums[j];                    cur[2] = nums[k];                    ret.push_back(cur);                    j ++;                    k --;                    //skip same j                    while(j < k && nums[j] == nums[j-1])                        j ++;                    //skip same k                    while(k > j && nums[k] == nums[k+1])                        k --;                }                else if(sum < 0)                {                    j ++;                    //skip same j                    while(j < k && nums[j] == nums[j-1])                        j ++;                }                else                {                    k --;                    //skip same k                    while(k > j && nums[k] == nums[k+1])                        k --;                }            }        }        return ret;    }};