leetcode 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> &num) {             vector<vector<int> > vResult;    vResult.reserve(100);    sort(num.begin(), num.end());    for(size_t i = 0; i < num.size(); i++)    {        size_t j = i+1;        size_t k = num.size() - 1;if(i > 0 && num[i-1] == num[i]){continue;}        while(j < k)        {            if(j-1 > i && num[j] == num[j-1])            {                j++;                continue;            }            if(k+1 < num.size() && num[k] == num[k+1])            {                k--;                continue;            }            if(num[i] + num[j] + num[k] == 0)            {                vector<int> vInt;                vInt.reserve(3);                vInt.push_back(num[i]);                vInt.push_back(num[j]);                vInt.push_back(num[k]);                vResult.push_back(vInt);                j++;            }            else if(num[i] + num[j] + num[k] > 0)            {                k--;            }            else            {                j++;            }        }    }    return vResult;    }};