[leetcode]15. 3Sum(Java实现)

https://leetcode.com/problems/3sum/#/description

Given an array S of n integers, are there elements a, b, c in S 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.

For example, given array S = [-1, 0, 1, 2, -1, -4],

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

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Java code：

package go.jacob.day618;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Demo2 {
	public List<List<Integer>> threeSum(int[] nums) {
		List<List<Integer>> result = new ArrayList<List<Integer>>();
		if (nums == null || nums.length < 3)
			return result;
		Arrays.sort(nums);
		for (int i = 0; i < nums.length - 2; i++) {
			//如果nums[i]与前一元素相同，会造成重复
			if (i == 0 || (i > 0 && nums[i] != nums[i - 1])) {
				int left = i + 1, right = nums.length - 1, sum = 0 - nums[i];
				while (left < right) {
					if (nums[left] + nums[right] == sum) {
						result.add(Arrays.asList(nums[i], nums[left], nums[right]));
						left++;
						right--;
						while (left < right && nums[left] == nums[left - 1])
							left++;
						while (right > left && nums[right] == nums[right + 1])
							right--;
					} else if (nums[left] + nums[right] > sum)
						right--;
					else
						left++;
				}
			}
		}

		return result;
	}
}