3Sum

Find unique 3sum: https://oj.leetcode.com/problems/3sum/

import java.util.Arrays;

public class Solution {

    public List<List<Integer>> threeSum(int[] num, int k) {
        List<List<Integer>> result = new ArrayList();
        if(num.length < 3) return result;

        Arrays.sort(num);
        for(int i = 0; i < num.length; i ++) {
            if(i > 0 && num[i] == num[i-1]) continue;
            int target = k - num[i];
            for(int m = i + 1, n = num.length - 1; m < n;) {
                int sum = num[m] + num[n];
                if( sum == target) {
                    List<Integer> list = new ArrayList();
                    list.add(num[i]);
                    list.add(num[m]);
                    list.add(num[n]);
                    result.add(list);
                    do { m ++; } while(m < n && num[m] == num[m - 1]);
                    do { n --; } while(m < n && num[n] == num[n + 1]);
                } else if(sum > target)
                    do { n --; } while(m < n && num[n] == num[n + 1]);
                  else
                    do { m ++; } while(m < n && num[m] == num[m - 1]);
            }
        }
        return result;
    }
}