LeetCode-15. 3Sum

Given an array ​​nums​​ of n integers, are there elements a, b, c in ​​nums​​ such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Note:

The solution set must not contain duplicate triplets.

Example:

Given array nums = [-1, 0, 1, 2, -1, -4],

A solution set is:
[
  [-1, 0, 1],
  [-1, -1, 2]
]

题解：

去重参考了讨论区，只想到了set暴力去重，132ms。

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