2149.RearrangeArray.cs

// 2149. Rearrange Array Elements by Sign
// You are given a 0-indexed integer array nums of even length consisting of an equal number of positive and negative integers.
// You should return the array of nums such that the the array follows the given conditions:
// Every consecutive pair of integers have opposite signs.
// For all integers with the same sign, the order in which they were present in nums is preserved.
// The rearranged array begins with a positive integer.
// Return the modified array after rearranging the elements to satisfy the aforementioned conditions.

// Example 1:
// Input: nums = [3,1,-2,-5,2,-4]
// Output: [3,-2,1,-5,2,-4]
// Explanation:
// The positive integers in nums are [3,1,2]. The negative integers are [-2,-5,-4].
// The only possible way to rearrange them such that they satisfy all conditions is [3,-2,1,-5,2,-4].
// Other ways such as [1,-2,2,-5,3,-4], [3,1,2,-2,-5,-4], [-2,3,-5,1,-4,2] are incorrect because they do not satisfy one or more conditions.  

// Example 2:
// Input: nums = [-1,1]
// Output: [1,-1]
// Explanation:
// 1 is the only positive integer and -1 the only negative integer in nums.
// So nums is rearranged to [1,-1].

// Constraints:
// 2 <= nums.length <= 2 * 105
// nums.length is even
// 1 <= |nums[i]| <= 105
// nums consists of equal number of positive and negative integers.

public class Solution {
    public int[] RearrangeArray(int[] nums) {
        int[] res = new int[nums.Length];
        int i = 0, pos = 0, neg = 1;
        while(i < nums.Length){
            if(nums[i] >= 0){
                res[pos] = nums[i];
                pos += 2;
            }
            else{
                res[neg] = nums[i];
                neg += 2;
            }
            i++;
        }
        return res;
    }
}