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)

最主要的是对相同的数据进行处理。

class Solution {public:    vector<vector<int> > threeSum(vector<int> &num) {        sort(num.begin(),num.end());        vector<vector<int> >result;        vector<int>temp;        int n = num.size();        if(n < 3){            return result;        }        for(int i=0; i<n-2 && num[i]<=0; ++i){            if(i > 0 && num[i]==num[i-1]){               continue;             }            int j= i + 1;            int k= n - 1;            while(j < k)            {                if(j > i + 1 && num[j] == num[j - 1]){                    j++;                    continue;                }                if(k < n - 1 && num[k] == num[k + 1]){                    k--;                    continue;                }                int sum = num[i] + num[j] + num[k];                if(sum < 0){                  j++;                }                else if(sum > 0){                  k--;                }                else if(sum == 0)                {                     temp.clear();                     temp.push_back(num[i]);                     temp.push_back(num[j]);                     temp.push_back(num[k]);                     result.push_back(temp);                     j++;                     k--;                }            }        }        return result;    }};