LeetCode 561. Array Partition I

Given an array of 2n integers, your task is to group these integers into n pairs of integer, say (a₁, b₁), (a₂, b₂), ..., (a_n, b_n) which makes sum of min(a_i, b_i) 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:

1. n is a positive integer, which is in the range of [1, 10000].
2. All the integers in the array will be in the range of [-10000, 10000].

Java：

class Solution {
    public int arrayPairSum(int[] nums) {
        int sum = 0;
        quickSort(nums,0,nums.length - 1);
        for (int i = 0; i < nums.length; i += 2) {
            sum += nums[i];
        }
        return sum;
    }
     public void quickSort(int[] array, int low, int high) {
            if (low > high) return;
            int i = low;
            int j = high;
            int temp = array[low];
            while (i != j) {
                while (array[j] >= temp && i < j) {
                    j--;
                }
                while (array[i] <= temp && i < j) {
                    i++;
                }
                if (array[i] > array[j]) {
                    int tem = array[i];
                    array[i] = array[j];
                    array[j] = tem;
                }
            }
            array[low] = array[i];
            array[i] = temp;
            quickSort(array,low,j - 1);
            quickSort(array,i + 1,high);
            return;
        }
}