2.1.8 —线性表—3Sum

描述
Given an array S of n integers, are there elementsa, b, cinSsuch thata+b+c= 0? Find all uniquetriplets 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)

#include<iostream>#include<vector>#include<algorithm>using namespace std;class ThreeSum{private:void Sort(int a[], int n);vector<pair<int, int>> TwoSumIsValue(int a[], int begin, int end, int value);public:vector<vector<int>> ThreeSumIsValue(int a[], int n, int value);};void ThreeSum::Sort(int a[], int n){for (int i = 0; i < n-1; i++){int min =i;for (int j=i; j < n; j++){if (a[j] < a[min])min = j;}if (min != i){int temp = a[i];a[i] = a[min];a[min] = temp;}}}vector<pair<int, int>> ThreeSum::TwoSumIsValue(int a[], int begin, int end, int value){vector<pair<int, int>> res;res.clear();if (begin >= end)return res;//while (begin < end){if (a[begin] + a[end] == value){res.push_back(make_pair(begin, end));begin++;end--;}else if (a[begin] + a[end]<value){begin++;}else{end--;}}return res;}vector<vector<int>> ThreeSum::ThreeSumIsValue(int a[], int n, int value){vector<vector<int>> res;res.clear();if (n <= 2)return res;//Sort(a, n);for (int i = 0; i < n - 2; i++){int temp = value - a[i];vector<pair<int, int>> res2 = TwoSumIsValue(a, i + 1, n-1, temp);if (res2.size()>0){for (int j = 0; j < res2.size(); j++){vector<int> temp_res;temp_res.push_back(a[i]);temp_res.push_back(a[res2[j].first]);temp_res.push_back(a[res2[j].second]);res.push_back(temp_res);}}}sort(res.begin(), res.end());res.erase(unique(res.begin(), res.end()), res.end());return res;}int main(){const int n = 10;int a[n] = { 3, 8, -14, -14, 4, 6, 1, 9, 5, 7 };ThreeSum threesum;int value = 0;vector<vector<int>> res = threesum.ThreeSumIsValue(a, n, value);for (int i = 0; i < res.size(); i++){for (int j = 0; j < res[i].size(); j++)cout << res[i][j] << " ";cout << endl;}}