LeetCode #15 3Sum

Description

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.

---

Analysis

题目难度为：Medium
本题思路，取出a，然后将剩下的n-1个数和b+c变为2Sum问题。同理也适用于4Sum问题等

---

Code（c++)

class Solution {public:    vector<vector<int>> threeSum(vector<int>& nums) {        vector<vector<int>> res;        sort(nums.begin(), nums.end());        for (int k = 0; k < nums.size(); ++k) {            if (nums[k] > 0) break;            if (k > 0 && nums[k] == nums[k - 1]) continue;            int target = 0 - nums[k];            int i = k + 1, j = nums.size() - 1;            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 + 1]) ++i;                    while (i < j && nums[j] == nums[j - 1]) --j;                    ++i; --j;                } else if (nums[i] + nums[j] < target) ++i;                else --j;            }        }        return res;    }};