[数据结构与算法]15. 三数之和

15. 三数之和

class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        Arrays.sort(nums); //O(nlogn)

        for(int i = 0;i < nums.length; i++){//O(n^2)
            if (nums[i] > 0){return result;}

            if (i > 0 && nums[i] == nums[i-1]){continue;}//去掉重复

            int left = i + 1;
            int right = nums.length - 1;
            while (right > left){
                int sum = nums[i] + nums[left] + nums[right];
                if(sum > 0){
                    right--;
                }else if(sum < 0){
                    left++;
                }else {
                    result.add(Arrays.asList(nums[i],nums[left],nums[right]));

                    while (right > left && nums[right] == nums[right - 1]) right--; //去掉重复
                    while (right > left && nums[left] == nums[left + 1]) left++;  //去掉 重复

                    right--;
                    left++;
                }
            }
        }
        return result;
    }
}