leetcode-15-java

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]
]

public static List<List<Integer>> threeSum(int[] nums) {
    List<List<Integer>> list = new ArrayList<>();
    if (null == nums || nums.length < 3) {
        return list;
    }

    //jdk自带的快速排序
    //Arrays.sort(nums);
    insertSort(nums);

    int right = nums.length - 1;
    for (int i = 0; i < nums.length - 2; i++) {
        if (i > 0 && nums[i] == nums[i - 1]) {
            continue;
        }
        twoSum(list, nums, -1 * nums[i], i + 1, right);
    }

    return list;
}

private static void twoSum(List<List<Integer>> list, int[] nums, int target, int left , int right) {
    while (left < right) {
        int tmp = nums[left] + nums[right];
        if (tmp == target) {
            list.add(Arrays.asList(-target, nums[left], nums[right]));


            while (left < right && nums[left] == nums[left + 1]) {
                left ++;
            }

            while (right > left && nums[right] == nums[right - 1]) {
                right --;
            }

            left ++;
            right--;
        } else if (tmp > target) {
            right --;
        } else if (tmp < target) {
            left ++;
        }
    }
}



//插入排序
private static void insertSort(int[] arrs) {
    for (int i = 1; i < arrs.length; i++) {
        int index = i;
        int cur = arrs[index];
        while (index > 0) {
            if (cur < arrs[index - 1]) {
                arrs[index] = arrs[index - 1];
                index --;
            } else {
                break;
            }

        }
        arrs[index] = cur;
    }
}