ArrayPartitionI.cpp

//Given an array of 2n integers, your task is to group these integers into n pairs of integer, say (a1, b1), (a2, b2), ..., (an, bn) which makes sum of min(ai, bi) for all i from 1 to n as large as possible.
//
//Example 1:
//Input: [1,4,3,2]
//
//Output: 4
//Explanation: n is 2, and the maximum sum of pairs is 4 = min(1, 2) + min(3, 4).
//Note:
//n is a positive integer, which is in the range of [1, 10000].
//All the integers in the array will be in the range of [-10000, 10000].


#include<vector>
#include<iostream>
#include<algorithm>

using namespace std;

class ArrayPartitionI
{
public:
	int arrayPairSum(vector<int>& nums) {
		/*sort(nums.begin(), nums.end());
		int res = 0;
		for (int i = 0; i<nums.size(); i += 2)
			res += nums[i];
		return res;*/


		//bucker sort
		vector<int> t(20001, 0);
		for (size_t i = 0; i < nums.size(); i++)
		{
			++t[nums[i] + 10000];
		}
		bool flag = true;
		int res=0;
		for (size_t i = 0; i < t.size(); )
		{
			if (t[i]>0 && flag)
			{
				res += i - 10000;
				--t[i];
				flag = false;
			}
			else if (t[i]>0 && !flag)
			{
				--t[i];
				flag = true;
			}
			else
			{
				++i;
			}
		}
		return res;
	}

};


void main_ArrayPartitionI()
{
	vector<int> nums = vector<int>{1,4,3,2};
	ArrayPartitionI nb;
	
	cout << nb.arrayPairSum(nums) << endl;



}