15.3Sum (Two-Pointers)

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.

思路：首先大循环第一个数，从第一个数之后首尾指针向中间夹逼，时间复杂度O(n2)。需要注意跳过重复的数字。

class Solution {

public:

    vector<vector<int>> threeSum(vector<int>& nums) {

        int size = nums.size();

        if(size < ) return result;

        sort(nums.begin(), nums.end());

        find(nums, , size-, -nums[]);

        for(int i = ; i < size-; i++){

            if(nums[i]!=nums[i-]) find(nums, i+, size-, -nums[i]);

        }

        return result;

    }

    void find(vector<int>& nums, int start, int end, int target){

        int sum;

        while(start<end){

            sum = nums[start]+nums[end];

            if(sum == target){

                item.clear();

                item.push_back(-target);

                item.push_back(nums[start]);

                item.push_back(nums[end]);

                result.push_back(item);

                do{

                    start++;

                }while(start!= end && nums[start] == nums[start-]);

                do{

                    end--;

                }while(end!=start && nums[end] == nums[end+]);

            }

            else if(sum>target){

                do{

                    end--;

                }while(end!=start && nums[end] == nums[end+]);

            }

            else{

                do{

                    start++;

                }while(start!= end && nums[start] == nums[start-]);

            }

        }

    }

private:

    vector<vector<int>> result;

    vector<int> item;

};

巴特西

15.3Sum (Two-Pointers)

最新文章

热门文章