LeetCode 015 3Sum

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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.

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        vector<vector<int>> result;
        int size = nums.size();
        if(size <= 2) return result;
        
        sort(nums.begin(), nums.end());
        
        for(int i = 0; i < size - 2; i++) {
            int a = nums[i];
            if(a > 0) break; // 最小的a>0，直接退出
            if(i > 0 && a == nums[i - 1]) continue; // 此数字为a，上一次循环已考虑过，不能重复
            for(int j = i + 1, k = size - 1; j < k;) {
                int b = nums[j], c = nums[k];
                int value = a + b + c;
                if(value == 0) {
                    result.push_back(vector<int>{a, b, c});
                    while(b == nums[j]) j++; // 为了避免重复数字
                    while(c == nums[k]) k--;
                } else if(value > 0) { // 正数过大
                    k--;
                } else { // 正数过小
                    j++;
                }
            }
        }
        return result;
    }
};