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:
For example, given array S = {-1 0 1 2 -1 -4}, A solution set is: (-1, 0, 1) (-1, -1, 2)Analysis
Two-pointer scan
O(n^2)
c++
vector<vector<int> > threeSum(vector<int> &num) { vector<vector<int>> result; sort(num.begin(),num.end()); for(int i=0; i<num.size(); i++){ int target = 0-num[i]; int start = i+1; int end = num.size()-1; while(start<end){ if(num[start]+ num[end] == target){ vector<int> solution; solution.push_back(num[i]); solution.push_back(num[start]); solution.push_back(num[end]); result.push_back(solution); start++, end--; while(start<end && num[start] == num[start-1]) start++; while(start<end && num[end] == num[end+1]) end--; } else if(num[start] + num[end] >target) end--; else start++; } while(i<num.size() && num[i] == num[i+1]) i++; } return result; }java
public List<List<Integer>> threeSum(int[] num) { List<List<Integer>> result = new ArrayList<List<Integer>>(); Arrays.sort(num); int len = num.length; for(int i=0;i<len;i++){ int target = 0-num[i]; int start = i+1, end = len-1; while(start<end){ if(num[start]+num[end]==target){ ArrayList<Integer> content = new ArrayList<>(); content.add(num[i]); content.add(num[start]); content.add(num[end]); result.add(content); start++; end--; while(start<end &&num[start]==num[start-1]) start++; while(start<end && num[end] == num[end+1]) end--; } else if(num[start]+num[end]>target){ end--; } else { start++; } } while(i<len-1 && num[i]==num[i+1]) i++; } return result; }
用暴力搜索,三个循环,O(n^3)不能通过大数据
public List<List<Integer>> threeSum(int[] num) { List<List<Integer>> result = new ArrayList<List<Integer>>(); for(int i=0;i<num.length;i++){ int temp = 0-num[i]; for(int j=i+1;j<num.length;j++){ for(int k=j+1;k<num.length;k++){ if(num[j]+num[k]==temp){ ArrayList<Integer> content = new ArrayList<>(); content.add(i); content.add(j); content.add(k); result.add(content); } } } } return result; }