leetCode 15. 3Sum

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.

Example:

Given array nums = [-1, 0, 1, 2, -1, -4],

A solution set is:
[
  [-1, 0, 1],
  [-1, -1, 2]
]

有空没空也得记得刷道题啊，不然乍一敲代码手生的很啊。

class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        List<List<Integer>> list = new ArrayList<>();//存放List<Integer>数组元素
        Arrays.sort(nums);
        int length = nums.length;
        for (int i = 0; i < length-2; i++) {
            if (i != 0 && nums[i] == nums[i-1])
                continue;
            for (int j = i+1; j < length-1; j++) {
                if (nums[i] + nums[j] + nums[length-1] < 0)
                    continue;
                int th = nums[i] + nums[j];
                if(th > 0)//确保nums[i]+nums[j] < 0
                    continue;

                for (int i1 = nums.length - 1; i1 > j; i1--) {
                    if (nums[i1] + th == 0) {
                        if (list.size() > 0) {
                            List<Integer> l = list.get(list.size()-1);
                            if (l.get(0) == nums[i] && l.get(1) == nums[j] && l.get(2) == nums[i1]) {
                                break;
                            }
                        }
                        ArrayList<Integer> listElem = new ArrayList<>();
                        listElem.add(nums[i]);
                        listElem.add(nums[j]);
                        listElem.add(nums[i1]);
                        list.add(listElem);
                        break;
                    }
                    else if (nums[i1] + th < 0)
                        break;
                }
            }
        }

        return list;
    }
}