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  • leetcode 3sum

    Given an array S of n integers, are there elements abc 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;
        }
    }
    

      

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  • 原文地址:https://www.cnblogs.com/lilyfindjobs/p/4187957.html
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