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leetcode 3sum
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)
使用两个标记，left和right， 对于每一个值，分别从左向右，从右向左计算
！！ 如何消除duplicate 不太会！！！public class Solution { public ArrayList<ArrayList<Integer>> threeSum(int[] num) { ArrayList<ArrayList<Integer>> result=new ArrayList<ArrayList<Integer>>(); if(num==null||num.length<3){ return result; } int sum=0; Arrays.sort(num); for(int i=0;i<num.length-2;i++){ if (i != 0 && num[i] == num[i - 1]) { continue; // to skip duplicate numbers; e.g [0,0,0,0] } int left=i+1; int right=num.length-1; while(left<right){ sum=num[i]+num[left]+num[right]; if(sum==0){ ArrayList<Integer> temp=new ArrayList<Integer>(); temp.add(num[i]); temp.add(num[left]); temp.add(num[right]); result.add(temp); left++; right--; while (left < right && num[left] == num[left - 1]) { // to skip duplicates left++; } while (left < right && num[right] == num[right + 1]) { // to skip duplicates right--; } } else if(sum<0){ left++; } else{ right--; } } } return result; }}
leetcode 3sum
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