• 題目：給定一個數組，找出所有不重複的三元組，使用三元組的加和為0
• 難度：Medium
• 思路：先對陣列排序，迴圈遍歷陣列，然後每次迴圈nums[i]定義兩個指標，判斷指標所指元素相加是否等於-nums[i]
• 程式碼：

public class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        if(nums == null || nums.length < 3
 
){
            return result;
        }
        Arrays.sort(nums);
        if(nums[0] > 0){
            return result;
        }

        for(int i = 0; i < nums.length; i++){
            int sum = 0-nums[i];
            int low = i+1;
            int high = nums.length-1;
            if((i == 0 || (i > 0
 
 && nums[i] != nums[i-1])) && nums[i] <= 0){

                while(low < high){
                    if(nums[low] + nums[high] == sum){
                        result.add(Arrays.asList(nums[i], nums[low], nums[high]));
                        while(low < high && nums[low] == nums[++low]);
                        while
 
(low < high && nums[high] == nums[--high]);
                    }else if(nums[low] + nums[high] > sum){
                        high--;
                    }else{
                        low++;
                    }
                }
            }
        }
        return result;
    }
}