leetcode.561 Array Partition I

Question

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.

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].

Solution

int compare( const void* a, const void* b)
{
     int int_a = * ( (int*) a );
     int int_b = * ( (int*) b );

     if ( int_a == int_b ) return 0;
     else if ( int_a < int_b ) return -1;
     else return 1;
}

int arrayPairSum(int* nums, int numsSize) {
    int sum = 0;
    if (numsSize == 0) return 0;
    
    qsort( nums, numsSize, sizeof(int), compare );
    
    int i;
    for (i = 0; i < numsSize; i+=2)
        sum+=nums[i];

    return sum;
}