[code random entry - hash table] T15, sum of three numbers - double pointer + sort

T15、 Sum of three numbers

Give you one containing n Array of integers nums, Judge nums Are there three elements in a,b,c , bring a + b + c = 0 ？ Please find out all and for 0 Triple without repetition .
Be careful ： Answer cannot contain duplicate triples .
source ： Power button （LeetCode）
link ：https://leetcode.cn/problems/3sum
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The hardest part of this question is how to deal with repeated results ;

So it's sort + The idea of double pointer

Recycle in the outer layer [0,n) determine a = nums[i], And then in i+1,n Use double pointers between

    public List<List<Integer>> threeSum(int[] nums) {
    
        int n = nums.length;
        List<List<Integer>> ret = new ArrayList<>();
        if(n < 3){
    
            return ret;
        }
        Arrays.sort(nums);
        // int i = 0, l = i+1, h = n-1;
        // a b c
        for(int i = 0; i < n; i++){
    
            if(nums[i] > 0){
    
                return ret;
            }
            if(i > 0 && nums[i] == nums[i-1]){
    
                continue;
            }
            int l = i+1, h = n-1;
            while(l < h){
    
                int a = nums[i];
                int b = nums[l];
                int c = nums[h];
                if(a + b + c == 0){
    
                    ret.add(Arrays.asList(a,b,c));
                    while(l < h && nums[h] == nums[h-1]){
    
                        h--;
                    }
                    while(l < h && nums[l] == nums[l+1]){
    
                        l++;
                    }
                    h--;
                    l++;
                }else if(a + b + c < 0){
    
                    l++;
                }else{
    
                    h--;
                }
            }
        }
        return ret;
    }