[LeetCode] 3Sum

来源：互联网发布：西南交大网络教学中心编辑：程序博客网时间：2024/04/28 02:35

Total Accepted: 12950 Total Submissions: 78829

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:

Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤ b ≤ c)
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)

public class Solution {    public ArrayList<ArrayList<Integer>> threeSum(int[] num) {        ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();        if (num.length < 3) return list;        Arrays.sort(num);        int sum = num[0] + num[1] + num[2];        int closest = sum;                for (int i = 0; i < num.length - 2; i++) {            // skip replicated numbers            if (i > 0 && num[i - 1] == num[i]) continue;            if (num[i] > 0) break;                        int lo = i + 1;            int hi = num.length - 1;                        while (lo < hi) {                // skip replicated numbers                while (lo < num.length - 1 && lo > i + 1 && num[lo] == num[lo-1]) lo++;                while (hi < num.length - 1 && hi > i + 1 && num[hi] == num[hi+1]) hi--;                if (lo >= hi) break;                                sum = num[i] + num[lo] + num[hi];                  closest = Math.abs(sum) < Math.abs(closest) ? sum : closest;                                  if      (sum > 0)   hi--;                  else if (sum < 0)   lo++;                  else {                    ArrayList<Integer> triplet = new ArrayList<Integer>();                    triplet.add(num[i]);                    triplet.add(num[lo]);                    triplet.add(num[hi]);                                        list.add(triplet);                    hi--;                    lo++;                }            }        }                return list;    }}

0 0