solve.cpp

#include <vector>
#include <map>
#include <set>
#include <cstdio>
#include <algorithm>
using namespace std;
class Solution {
	public:
		vector<vector<int>> fourSum(vector<int> &num, int target)
		{
			vector<vector<int>> result;
			int n = num.size();
			if (n < 4)
				return result;
			sort(num.begin(), num.end());
			for (int i = 0; i < n - 3; ++i) {
				if (i > 0 && num[i] == num[i - 1])
					continue;
				vector<int> n(num.begin() + i + 1, num.end());
				vector<vector<int>> ret = threeSum(n, target - num[i]);
				for (auto v : ret)
				{
					v.insert(v.begin(), num[i]);
					result.push_back(v);
				}
			}
			return result;
		}
		vector<vector<int>> threeSum(vector<int> &num, int target) {
		//	sort(num.begin(), num.end());
			vector<vector<int>> result;
			auto n = num.size();
			size_t i;
			for (i = 0; i < n; ++i) {
				if (i > 0 && num[i] == num[i - 1])
					continue;
				int a = num[i];
				int low = i + 1, high = n - 1;
				while (low < high) {
					int b = num[low];
					int c = num[high];
					if (a + b + c == target) {
						vector<int> v = {a, b, c};
						result.push_back(v);
						while (low + 1 < n && num[low] == num[low + 1]) low++;
						while (high - 1 >= 0 && num[high] == num[high - 1]) high--;
						low++;
						high--;
					} else if (a + b + c > target) {
						while (high - 1 >= 0 && num[high] == num[high - 1]) high--;
						high--;
					} else {
						while (low + 1 < n && num[low] == num[low + 1]) low++;
						low++;
					}
				}
			}
			return result;
		}
};
int main(int argc, char **argv)
{
	vector<int> S = {1,0,-1,0,-2,2};
	Solution solution;
	auto result = solution.fourSum(S, 0);
	for (auto v : result) {
		for_each(v.begin(), v.end(), [=](int i){printf("%d ", i);});
		printf("\n");
	}
}