LeetCode 15. 3Sum [Medium]

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题目来源：https://leetcode.com/problems/3sum/

题目难度：Medium

解答1[Java]：

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class Solution {
    public List<List<Integer>> threeSum(int[] num) {
        Arrays.sort(num);
        List<List<Integer>> res = new LinkedList<>();
        for (int i = 0; i < num.length - 2; i++) {
            if (i == 0 || (i > 0 && num[i] != num[i - 1])) {
                int lo = i + 1, hi = num.length - 1, sum = 0 - num[i];
                while (lo < hi) {
                    if (num[lo] + num[hi] == sum) {
                        res.add(Arrays.asList(num[i], num[lo], num[hi]));
                        while (lo < hi && num[lo] == num[lo + 1])
                            lo++;
                        while (lo < hi && num[hi] == num[hi - 1])
                            hi--;
                        lo++;
                        hi--;
                    } else if (num[lo] + num[hi] < sum)
                        lo++;
                    else
                        hi--;
                }
            }
        }
        return res;
    }
}