C++ 解法, 执行用时: 2ms, 内存消耗: 384KB, 提交时间: 2021-06-20

class Solution {
    public:
    vector<vector<int> > threeSum(vector<int> &num) {
        vector<vector<int>> ret = {};
        int sz = num.size();
        if (sz < 3) return ret;
        //先排序
        sort(num.begin(), num.end());
        //遍历数组 选为target 跳过重复
        for (int i = 0; i < sz - 2; i++) {
            int l = i + 1; //左指针
            int r = sz - 1; //右指针
            int tar = -num[i]; //target
            while (l < r) {
                if (num[l] + num[r] > tar) { //太大了 小一点
                    r--;
                }else if (num[l] + num[r] < tar) { //太小了 大一点
                    l++;
                }else { //正好找到家和为-tar的组合
                    vector<int> tmp_ret = {num[i], num[l], num[r]};
                    ret.push_back(tmp_ret);
                    //使l,r跳过重复项
                    while (r - 1 > l && num[r - 1] == num[r]) r--;
                    while (l + 1 < r && num[l + 1] == num[l]) l++;
                    r--, l++;
                }
            }
            //遍历i时防止重复项
            while (i + 1 < sz - 2 && num[i] == num[i + 1])
                i++;
        }
        return ret;
    }
};

C++ 解法, 执行用时: 2ms, 内存消耗: 388KB, 提交时间: 2021-07-20

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

C++ 解法, 执行用时: 2ms, 内存消耗: 396KB, 提交时间: 2022-02-09

class Solution {
public:
    vector<vector<int> > threeSum(vector<int> &num) {
        sort(num.begin(), num.end());//开始进行从小到大进行排序
        vector<vector<int> > res;
        if (num.size() < 3) return res;//小于三个直接返回false 进行特判
        for (int i=0;i<num.size()-2;i++) {
            int j=i+1;
            int k=num.size()-1;
            int target=-num[i];//预先减去遍历元素的大小
            //双指针操作
            while (j<k) {
                if (num[j]+num[k]>target) k--;//结果大于目标值 右指针左移
                else if (num[j]+num[k]<target) j++;//结果小于目标值 左指针左移
                else {
                    vector<int> current = {num[i], num[j], num[k]};
                    res.push_back(current);
                    //都是为了防止重复
                    while (j+1<k&&num[j+1]==num[j]) j++;
                    while (k-1>j&&num[k-1]==num[k]) k--;
                    j++;
                    k--;
                }
            }
            //防止重复
            while(i+1<num.size()-2&&num[i+1]==num[i]) i++;
        }
        return res;
    }
};

C++ 解法, 执行用时: 2ms, 内存消耗: 396KB, 提交时间: 2021-09-13

class Solution {
public:
    vector<vector<int> > threeSum(vector<int> &nums) {
        int n=nums.size();
        if(n<3)return {};
        sort(nums.begin(),nums.end());
         vector<vector<int> >ans;
        for(int i=0;i<n-2;++i){
            if(nums[i]>0)break;
            if(i>=1&&nums[i]==nums[i-1])continue;
            int l=i+1;
            int r=n-1;
            while(l<r){
                if(nums[i]+nums[l]+nums[r]==0){
                    ans.emplace_back(vector<int>{nums[i],nums[l],nums[r]});
                    l++;
                    r--;
                    while(l<r&&nums[l]==nums[l-1])++l;
                    while(i<r&&nums[r]==nums[r+1])r--;
                }
                else if(nums[i]+nums[l]+nums[r]<0)++l;
                else r--;
            }
        }
        return ans;
    }
};

C++ 解法, 执行用时: 2ms, 内存消耗: 396KB, 提交时间: 2021-09-01

class Solution {
public:
    vector<vector<int> > threeSum(vector<int> &num) {
        sort(num.begin(), num.end());
        vector<vector<int>> vec;
        int len = num.size(), l, r;
        for(int i = 0; i < len; i++){
            if(i != 0 && num[i]==num[i-1]) continue;
            int l = i + 1;
            int r = len - 1;
            while(l < r){
                if(num[i] + num[l] + num[r] ==0){
                    vec.push_back({num[i], num[l], num[r]});
                    l++;
                    r--;
                while(l < len && num[l] == num[l-1]) l++;//去重
                while(r > l && num[r] == num[r+1]) r--;
                }
                else if(num[i]+num[l]+num[r]>0){
                    r--;
                }
                else{
                    l++;
                }
            }
        }
        return vec;
    }
};