var threeSum = function(nums) {
    let ans = [];
    const len = nums.length;
    if(nums==null || len<3) {
        return ans;
    }
    nums.sort((a,b) => a-b);
    for (let i=0; i<len; i++) {
        let num = nums[i];
        if(num > 0){
            break;
        }
        if(i>0 && num==nums[i-1]) {
            continue;
        }
        let L = i+1;
        let R = len-1;
        while(L < R){
            const sum = num + nums[L]+nums[R];
            if(sum == 0){
                ans.push([nums[i],nums[L],nums[R]]);
                while (L<R && nums[L] == nums[L+1]) L++;
                while (L<R && nums[R] == nums[R-1]) R--; 
                L++;
                R--;
            }else if(sum<0){
                L++;
            }else if(sum>0){
                R--;
            }
        }
    }
    return ans;
}